diff --git a/l10n/ru.js b/l10n/ru.js
index 14ba864469..38ccff1ce8 100644
--- a/l10n/ru.js
+++ b/l10n/ru.js
@@ -115,6 +115,7 @@ OC.L10N.register(
     "Sorting" : "Сортировка",
     "Newest" : "Более новые",
     "Oldest" : "Более старые",
+    "Gravatar settings" : "Настройки Gravatar",
     "Use Gravatar and favicon avatars" : "Использовать значки Gravatar и favicon",
     "Register as application for mail links" : "Зарегистрировать в качестве приложения для обработки почтовых ссылок",
     "Register" : "Регистрация",
diff --git a/l10n/ru.json b/l10n/ru.json
index 0d491062d0..54f15a4913 100644
--- a/l10n/ru.json
+++ b/l10n/ru.json
@@ -113,6 +113,7 @@
     "Sorting" : "Сортировка",
     "Newest" : "Более новые",
     "Oldest" : "Более старые",
+    "Gravatar settings" : "Настройки Gravatar",
     "Use Gravatar and favicon avatars" : "Использовать значки Gravatar и favicon",
     "Register as application for mail links" : "Зарегистрировать в качестве приложения для обработки почтовых ссылок",
     "Register" : "Регистрация",
diff --git a/lib/AppInfo/Application.php b/lib/AppInfo/Application.php
index d58f6f073e..48c85854f2 100644
--- a/lib/AppInfo/Application.php
+++ b/lib/AppInfo/Application.php
@@ -53,6 +53,7 @@
 use OCA\Mail\Listener\SpamReportListener;
 use OCA\Mail\Listener\UserDeletedListener;
 use OCA\Mail\Notification\Notifier;
+use OCA\Mail\Provider\MailProvider;
 use OCA\Mail\Search\FilteringProvider;
 use OCA\Mail\Search\Provider;
 use OCA\Mail\Service\Attachment\AttachmentService;
@@ -156,6 +157,9 @@ public function register(IRegistrationContext $context): void {
 			$context->registerSearchProvider(Provider::class);
 		}
 
+		// Added in version 4.0.0
+		$context->registerMailProvider(MailProvider::class);
+
 		$context->registerNotifierService(Notifier::class);
 
 		// bypass Horde Translation system
diff --git a/lib/Db/MailAccountMapper.php b/lib/Db/MailAccountMapper.php
index b42c1908c4..0e41bbe976 100644
--- a/lib/Db/MailAccountMapper.php
+++ b/lib/Db/MailAccountMapper.php
@@ -83,6 +83,27 @@ public function findByUserId(string $userId): array {
 		return $this->findEntities($query);
 	}
 
+	/**
+	 * Finds a mail account(s) by user id and mail address
+	 *
+	 * @since 4.0.0
+	 *
+	 * @param string $userId system user id
+	 * @param string $address mail address (e.g. test@example.com)
+	 *
+	 * @return MailAccount[]
+	 */
+	public function findByUserIdAndAddress(string $userId, string $address): array {
+		$qb = $this->db->getQueryBuilder();
+		$query = $qb
+			->select('*')
+			->from($this->getTableName())
+			->where($qb->expr()->eq('user_id', $qb->createNamedParameter($userId)))
+			->andWhere($qb->expr()->eq('email', $qb->createNamedParameter($address)));
+
+		return $this->findEntities($query);
+	}
+
 	/**
 	 * @throws DoesNotExistException
 	 * @throws MultipleObjectsReturnedException
diff --git a/lib/Provider/Command/MessageSend.php b/lib/Provider/Command/MessageSend.php
new file mode 100644
index 0000000000..6f747135a2
--- /dev/null
+++ b/lib/Provider/Command/MessageSend.php
@@ -0,0 +1,151 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * SPDX-FileCopyrightText: 2024 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+namespace OCA\Mail\Provider\Command;
+
+use OCA\Mail\Db\LocalAttachment;
+use OCA\Mail\Db\LocalMessage;
+use OCA\Mail\Exception\ClientException;
+use OCA\Mail\Exception\UploadException;
+use OCA\Mail\Service\AccountService;
+use OCA\Mail\Service\Attachment\AttachmentService;
+use OCA\Mail\Service\OutboxService;
+use OCP\AppFramework\Utility\ITimeFactory;
+use OCP\Mail\Provider\Exception\SendException;
+use OCP\Mail\Provider\IAddress;
+use OCP\Mail\Provider\IMessage;
+
+class MessageSend {
+
+	public function __construct(
+		protected ITimeFactory $time,
+		protected AccountService $accountService,
+		protected OutboxService $outboxService,
+		protected AttachmentService $attachmentService
+	) {
+	}
+
+	/**
+	 * Performs send operation
+	 *
+	 * @since 4.0.0
+	 *
+	 * @param string $userId system user id
+	 * @param string $serviceId mail account id
+	 * @param IMessage $message mail message object with all required parameters to send a message
+	 * @param array $options array of options reserved for future use
+	 *
+	 * @return LocalMessage
+	 *
+	 * @throws SendException on failure, check message for reason
+	 *
+	 */
+	public function perform(string $userId, string $serviceId, IMessage $message, array $options = []): LocalMessage {
+		// validate that at least one To address is present
+		if (count($message->getTo()) === 0) {
+			throw new SendException('Invalid Message Parameter: MUST contain at least one TO address with a valid address');
+		}
+		// validate that all To, CC and BCC have email address
+		$entries = array_merge($message->getTo(), $message->getCc(), $message->getBcc());
+		array_walk($entries, function ($entry) {
+			if (empty($entry->getAddress())) {
+				throw new SendException('Invalid Message Parameter: All TO, CC and BCC addresses MUST contain at least an email address');
+			}
+		});
+		// validate that all attachments have a name, type, and contents
+		$entries = $message->getAttachments();
+		array_walk($entries, function ($entry) {
+			if (empty($entry->getName()) || empty($entry->getType()) || empty($entry->getContents())) {
+				throw new SendException('Invalid Attachment Parameter: MUST contain values for Name, Type and Contents');
+			}
+		});
+		// retrieve user mail account details
+		try {
+			$account = $this->accountService->find($userId, (int)$serviceId);
+		} catch (ClientException $e) {
+			throw new SendException('Error: occurred while retrieving mail account details', 0, $e);
+		}
+		// convert mail provider message to mail app message
+		$localMessage = new LocalMessage();
+		$localMessage->setType($localMessage::TYPE_OUTGOING);
+		$localMessage->setAccountId($account->getId());
+		$localMessage->setSubject((string)$message->getSubject());
+		$localMessage->setBody((string)$message->getBody());
+		// disabled due to issues caused by opening these messages in gui
+		//$localMessage->setEditorBody($message->getBody());
+		$localMessage->setHtml(true);
+		$localMessage->setSendAt($this->time->getTime());
+		// convert mail provider addresses to recipient addresses
+		$to = $this->convertAddressArray($message->getTo());
+		$cc = $this->convertAddressArray($message->getCc());
+		$bcc = $this->convertAddressArray($message->getBcc());
+		// save attachments
+		$attachments = [];
+		try {
+			foreach ($message->getAttachments() as $entry) {
+				$attachments[] = $this->attachmentService->addFileFromString(
+					$userId,
+					(string)$entry->getName(),
+					(string)$entry->getType(),
+					(string)$entry->getContents()
+				);
+			}
+		} catch (UploadException $e) {
+			$this->purgeSavedAttachments($attachments);
+			throw new SendException('Error: occurred while saving mail message attachment', 0, $e);
+		}
+		// save message
+		$localMessage = $this->outboxService->saveMessage(
+			$account,
+			$localMessage,
+			$to,
+			$cc,
+			$bcc,
+			array_map(static fn (LocalAttachment $attachment) => $attachment->jsonSerialize(), $attachments)
+		);
+		// send message
+		try {
+			$localMessage = $this->outboxService->sendMessage($localMessage, $account);
+		} catch (\Throwable $e) {
+			throw new SendException('Error: occurred while sending mail message', 0, $e);
+		}
+
+		return $localMessage;
+	}
+
+	/**
+	 * Converts IAddress objects collection to plain array
+	 *
+	 * @since 4.0.0
+	 *
+	 * @param array<int,IAddress> $addresses collection of IAddress objects
+	 *
+	 * @return array<int, array{email: string, label?: string}> collection of addresses and labels
+	 */
+	protected function convertAddressArray(array $addresses): array {
+		return array_map(static function (IAddress $address) {
+			return !empty($address->getLabel())
+				? ['email' => (string)$address->getAddress(), 'label' => (string)$address->getLabel()]
+				: ['email' => (string)$address->getAddress()];
+		}, $addresses);
+	}
+
+	/**
+	 * Removes attachments from data store
+	 *
+	 * @since 4.0.0
+	 *
+	 * @param array<int, LocalAttachment> $attachments collection of local attachment objects
+	 */
+	protected function purgeSavedAttachments(array $attachments): void {
+		foreach ($attachments as $attachment) {
+			$this->attachmentService->deleteAttachment($attachment->getUserId(), $attachment->getId());
+		}
+	}
+
+}
diff --git a/lib/Provider/MailProvider.php b/lib/Provider/MailProvider.php
new file mode 100644
index 0000000000..29877ef17c
--- /dev/null
+++ b/lib/Provider/MailProvider.php
@@ -0,0 +1,167 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * SPDX-FileCopyrightText: 2024 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+namespace OCA\Mail\Provider;
+
+use OCA\Mail\Account;
+use OCA\Mail\Exception\ClientException;
+use OCA\Mail\Service\AccountService;
+use OCP\IL10N;
+use OCP\Mail\Provider\Address as MailAddress;
+use OCP\Mail\Provider\IProvider;
+use OCP\Mail\Provider\IService;
+use Psr\Container\ContainerInterface;
+use Psr\Log\LoggerInterface;
+
+class MailProvider implements IProvider {
+
+	public function __construct(
+		protected ContainerInterface $container,
+		protected AccountService $accountService,
+		protected LoggerInterface $logger,
+		protected IL10N $l10n
+	) {
+	}
+
+	/**
+	 * Arbitrary unique text string identifying this provider
+	 *
+	 * @since 4.0.0
+	 *
+	 * @return string id of this provider (e.g. UUID or 'IMAP/SMTP' or anything else)
+	 */
+	public function id(): string {
+		return 'mail-application';
+	}
+
+	/**
+	 * Localized human friendly name of this provider
+	 *
+	 * @since 4.0.0
+	 *
+	 * @return string label/name of this provider (e.g. Plain Old IMAP/SMTP)
+	 */
+	public function label(): string {
+		return $this->l10n->t('Mail Application');
+	}
+
+	/**
+	 * Determine if any services are configured for a specific user
+	 *
+	 * @since 4.0.0
+	 *
+	 * @param string $userId system user id
+	 *
+	 * @return bool true if any services are configure for the user
+	 */
+	public function hasServices(string $userId): bool {
+		return (count($this->listServices($userId)) > 0);
+	}
+
+	/**
+	 * Retrieve collection of services for a specific user
+	 *
+	 * @since 4.0.0
+	 *
+	 * @param string $userId system user id
+	 *
+	 * @return array<string,IService> collection of service id and object ['1' => IServiceObject]
+	 */
+	public function listServices(string $userId): array {
+		// retrieve service(s) details from data store
+		$accounts = $this->accountService->findByUserId($userId);
+		// construct temporary collection
+		$services = [];
+		// add services to collection
+		foreach ($accounts as $entry) {
+			$services[(string)$entry->getId()] = $this->serviceFromAccount($userId, $entry);
+		}
+		// return list of services for user
+		return $services;
+	}
+
+	/**
+	 * Retrieve a service with a specific id
+	 *
+	 * @since 4.0.0
+	 *
+	 * @param string $userId system user id
+	 * @param string $serviceId mail account id
+	 *
+	 * @return IService|null returns service object or null if none found
+	 *
+	 */
+	public function findServiceById(string $userId, string $serviceId): IService|null {
+		// determine if a valid user and service id was submitted
+		if (empty($userId) && !ctype_digit($serviceId)) {
+			return null;
+		}
+		// retrieve service details from data store
+		try {
+			$account = $this->accountService->find($userId, (int)$serviceId);
+		} catch(ClientException $e) {
+			$this->logger->error('Error occurred while retrieving mail account details', [ 'exception' => $e ]);
+			return null;
+		}
+		// return mail service object
+		return $this->serviceFromAccount($userId, $account);
+	}
+
+	/**
+	 * Retrieve a service for a specific mail address
+	 *
+	 * @since 4.0.0
+	 *
+	 * @param string $userId system user id
+	 * @param string $address mail address (e.g. test@example.com)
+	 *
+	 * @return IService|null returns service object or null if none found
+	 */
+	public function findServiceByAddress(string $userId, string $address): IService|null {
+		// retrieve service details from data store
+		$accounts = $this->accountService->findByUserIdAndAddress($userId, $address);
+		// evaluate if service details where found
+		if (count($accounts) > 0) {
+			// return mail service object
+			return $this->serviceFromAccount($userId, $accounts[0]);
+		}
+
+		return null;
+	}
+
+	/**
+	 * Construct a new fresh service object
+	 *
+	 * @since 4.0.0
+	 *
+	 * @return IService fresh service object
+	 */
+	public function initiateService(): IService {
+		return new MailService($this->container);
+	}
+
+	/**
+	 * Construct a service object from a mail account
+	 *
+	 * @since 4.0.0
+	 *
+	 * @param string $userId system user id
+	 * @param Account $account mail account
+	 *
+	 * @return IService service object
+	 */
+	protected function serviceFromAccount(string $userId, Account $account): IService {
+		// extract values
+		$serviceId = (string)$account->getId();
+		$serviceLabel = $account->getName();
+		$serviceAddress = new MailAddress($account->getEmail(), $account->getName());
+		// return mail service object
+		return new MailService($this->container, $userId, $serviceId, $serviceLabel, $serviceAddress);
+	}
+
+}
diff --git a/lib/Provider/MailService.php b/lib/Provider/MailService.php
new file mode 100644
index 0000000000..22eb7f0b50
--- /dev/null
+++ b/lib/Provider/MailService.php
@@ -0,0 +1,182 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * SPDX-FileCopyrightText: 2024 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+namespace OCA\Mail\Provider;
+
+use OCA\Mail\Provider\Command\MessageSend;
+use OCP\Mail\Provider\Address;
+use OCP\Mail\Provider\Exception\SendException;
+use OCP\Mail\Provider\IAddress;
+use OCP\Mail\Provider\IMessage;
+use OCP\Mail\Provider\IMessageSend;
+use OCP\Mail\Provider\IService;
+use OCP\Mail\Provider\Message;
+
+use Psr\Container\ContainerInterface;
+
+class MailService implements IService, IMessageSend {
+
+	protected array $serviceSecondaryAddresses = [];
+	protected array $serviceAbilities = [];
+
+	public function __construct(
+		protected ContainerInterface $container,
+		protected string $userId = '',
+		protected string $serviceId = '',
+		protected string $serviceLabel = '',
+		protected IAddress $servicePrimaryAddress = new Address(),
+	) {
+		$this->serviceAbilities = ['MessageSend' => true];
+	}
+
+	/**
+	 * Arbitrary unique text string identifying this service
+	 *
+	 * @since 4.0.0
+	 *
+	 * @return string id of this service (e.g. 1 or service1 or anything else)
+	 */
+	public function id(): string {
+		return $this->serviceId;
+	}
+
+	/**
+	 * Checks if a service is able of performing an specific action
+	 *
+	 * @since 4.0.0
+	 *
+	 * @param string $value required ability e.g. 'MessageSend'
+	 *
+	 * @return bool true/false if ability is supplied and found in collection
+	 */
+	public function capable(string $value): bool {
+		// evaluate if required ability exists
+		if (isset($this->serviceAbilities[$value])) {
+			return (bool)$this->serviceAbilities[$value];
+		}
+		
+		return false;
+	}
+
+	/**
+	 * Retrieves a collection of what actions a service can perform
+	 *
+	 * @since 4.0.0
+	 *
+	 * @return array collection of abilities otherwise empty collection
+	 */
+	public function capabilities(): array {
+		return $this->serviceAbilities;
+	}
+
+	/**
+	 * Gets the localized human friendly name of this service
+	 *
+	 * @since 4.0.0
+	 *
+	 * @return string label/name of service (e.g. ACME Company Mail Service)
+	 */
+	public function getLabel(): string {
+		return $this->serviceLabel;
+	}
+
+	/**
+	 * Sets the localized human friendly name of this service
+	 *
+	 * @since 4.0.0
+	 *
+	 * @param string $value label/name of service (e.g. ACME Company Mail Service)
+	 *
+	 * @return self return this object for command chaining
+	 */
+	public function setLabel(string $value): self {
+		$this->serviceLabel = $value;
+		return $this;
+	}
+
+	/**
+	 * Gets the primary mailing address for this service
+	 *
+	 * @since 4.0.0
+	 *
+	 * @return IAddress mail address object
+	 */
+	public function getPrimaryAddress(): IAddress {
+		// retrieve and return primary service address
+		return $this->servicePrimaryAddress;
+	}
+
+	/**
+	 * Sets the primary mailing address for this service
+	 *
+	 * @since 4.0.0
+	 *
+	 * @param IAddress $value mail address object
+	 *
+	 * @return self return this object for command chaining
+	 */
+	public function setPrimaryAddress(IAddress $value): self {
+		$this->servicePrimaryAddress = $value;
+		return $this;
+	}
+
+	/**
+	 * Gets the secondary mailing addresses (aliases) collection for this service
+	 *
+	 * @since 4.0.0
+	 *
+	 * @return array<int, IAddress> collection of mail address object [IAddress, IAddress]
+	 */
+	public function getSecondaryAddresses(): array {
+		// retrieve and return secondary service addresses (aliases) collection
+		return $this->serviceSecondaryAddresses;
+	}
+
+	/**
+	 * Sets the secondary mailing addresses (aliases) for this service
+	 *
+	 * @since 4.0.0
+	 *
+	 * @param IAddress ...$value collection of one or more mail address object
+	 *
+	 * @return self return this object for command chaining
+	 */
+	public function setSecondaryAddresses(IAddress ...$value): self {
+		$this->serviceSecondaryAddresses = $value;
+		return $this;
+	}
+
+	/**
+	 * Construct a new fresh message object
+	 *
+	 * @since 30.0.0
+	 *
+	 * @return IMessage fresh message object
+	 */
+	public function initiateMessage(): IMessage {
+		return new Message();
+	}
+
+	/**
+	 * Sends an outbound message
+	 *
+	 * @since 4.0.0
+	 *
+	 * @param IMessage $message mail message object with all required parameters to send a message
+	 * @param array $options array of options reserved for future use
+	 *
+	 * @throws SendException on failure, check message for reason
+	 */
+	public function sendMessage(IMessage $message, array $options = []): void {
+		/** @var MessageSend $cmd */
+		$cmd = $this->container->get(MessageSend::class);
+		// perform action
+		$cmd->perform($this->userId, $this->serviceId, $message, $options);
+	}
+
+}
diff --git a/lib/Service/AccountService.php b/lib/Service/AccountService.php
index 1e88ad9921..dea1e33985 100644
--- a/lib/Service/AccountService.php
+++ b/lib/Service/AccountService.php
@@ -78,6 +78,35 @@ public function findById(int $id): Account {
 		return new Account($this->mapper->findById($id));
 	}
 
+	/**
+	 * Finds a mail account by user id and mail address
+	 *
+	 * @since 4.0.0
+	 *
+	 * @param string $userId system user id
+	 * @param string $address mail address (e.g. test@example.com)
+	 *
+	 * @return Account[]
+	 */
+	public function findByUserIdAndAddress(string $userId, string $address): array {
+		// evaluate if cached accounts collection already exists
+		if (isset($this->accounts[$userId])) {
+			// initialize temporary collection
+			$list = [];
+			// iterate through accounts and find accounts matching mail address
+			foreach ($this->accounts[$userId] as $account) {
+				if ($account->getEmail() === $address) {
+					$list[] = $account;
+				}
+			}
+			return $list;
+		}
+		// if cached accounts collection did not exist retrieve account details directly from the data store
+		return array_map(static function ($a) {
+			return new Account($a);
+		}, $this->mapper->findByUserIdAndAddress($userId, $address));
+	}
+
 	/**
 	 * @param string $userId
 	 * @param int $id
diff --git a/tests/Unit/Provider/Command/MessageSendTest.php b/tests/Unit/Provider/Command/MessageSendTest.php
new file mode 100644
index 0000000000..229f51d7a1
--- /dev/null
+++ b/tests/Unit/Provider/Command/MessageSendTest.php
@@ -0,0 +1,321 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * SPDX-FileCopyrightText: 2024 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+namespace OCA\Mail\Tests\Unit\Provider\Command;
+
+use ChristophWurst\Nextcloud\Testing\TestCase;
+use OCA\Mail\Account;
+use OCA\Mail\Db\LocalAttachment;
+use OCA\Mail\Db\LocalMessage;
+use OCA\Mail\Db\MailAccount;
+use OCA\Mail\Exception\ClientException;
+use OCA\Mail\Exception\UploadException;
+use OCA\Mail\Provider\Command\MessageSend;
+use OCA\Mail\Service\AccountService;
+use OCA\Mail\Service\Attachment\AttachmentService;
+use OCA\Mail\Service\OutboxService;
+use OCP\AppFramework\Utility\ITimeFactory;
+use OCP\Mail\Provider\Address;
+use OCP\Mail\Provider\Attachment;
+use OCP\Mail\Provider\Exception\SendException;
+use OCP\Mail\Provider\Message;
+use PHPUnit\Framework\MockObject\MockObject;
+
+class MessageSendTest extends TestCase {
+	
+	private IConfig&MockObject $config;
+	private ITimeFactory&MockObject $time;
+	private AccountService&MockObject $accountService;
+	private OutboxService&MockObject $outboxService;
+	private AttachmentService&MockObject $attachmentService;
+	private MessageSend $commandSend;
+	private Message $mailMessage;
+	private Attachment $mailAttachment;
+	private Account $localAccount;
+	private array $localMessageData;
+	private array $localAttachmentData;
+
+	protected function setUp(): void {
+		parent::setUp();
+		// construct mock constructor parameters
+		$this->time = $this->createMock(ITimeFactory::class);
+		$this->accountService = $this->createMock(AccountService::class);
+		$this->outboxService = $this->createMock(OutboxService::class);
+		$this->attachmentService = $this->createMock(AttachmentService::class);
+		// construct test object
+		$this->commandSend = new MessageSend($this->time, $this->accountService, $this->outboxService, $this->attachmentService);
+		// construct mail provider attachment
+		$this->mailAttachment = new Attachment(
+			'This is the contents of our plan',
+			'plan.txt',
+			'text/plain'
+		);
+		// construct mail provider message
+		$this->mailMessage = new Message();
+		$this->mailMessage->setFrom(new Address('user1@testing.com', 'User One'));
+		$this->mailMessage->setTo(new Address('user2@testing.com', 'User Two'));
+		$this->mailMessage->setSubject('World domination');
+		$this->mailMessage->setBodyPlain('I have the most brilliant plan. Let me tell you all about it. What we do is, we');
+		// construct mail app account object
+		$this->localAccount = new Account(new MailAccount([
+			'accountId' => 100,
+			'accountName' => 'User One',
+			'emailAddress' => 'user1@testing.com',
+			'imapHost' => '',
+			'imapPort' => '',
+			'imapSslMode' => false,
+			'imapUser' => '',
+			'smtpHost' => '',
+			'smtpPort' => '',
+			'smtpSslMode' => false,
+			'smtpUser' => '',
+		]));
+		// construct mail app message object
+		$this->localMessageData = [
+			'type' => 0,
+			'accountId' => 100,
+			'subject' => 'World domination',
+			'body' => 'I have the most brilliant plan. Let me tell you all about it. What we do is, we',
+			'html' => true
+		];
+		// construct mail app attachment object
+		$this->localAttachmentData = [
+			'id' => null,
+			'userId' => null,
+			'fileName' => 'event.ics',
+			'mimeType' => 'text/plain',
+			'createdAt' => null,
+			'localMessageId' => null
+		];
+	}
+
+	public function testPerformWithAttachment(): void {
+		// define time factory return
+		$this->time->method('getTime')->willReturn(1719792000);
+		// define account service returns
+		$this->accountService->method('find')->will(
+			$this->returnValueMap([
+				['user1', 100, $this->localAccount]
+			])
+		);
+		// construct mail app attachment
+		$localAttachmentReturned = $this->localAttachmentData;
+		$localAttachmentReturned['id'] = 1;
+		$localAttachmentReturned['userId'] = 'user1';
+		$localAttachmentReturned = LocalAttachment::fromParams($localAttachmentReturned);
+		// define attachment service returns
+		$this->attachmentService->expects($this->once())->method('addFileFromString')
+			->with(
+				'user1',
+				$this->mailAttachment->getName(),
+				$this->mailAttachment->getType(),
+				$this->mailAttachment->getContents()
+			)->willReturn($localAttachmentReturned);
+		// construct mail app message objects
+		$localMessageFresh = $this->localMessageData;
+		$localMessageFresh['sendAt'] = $this->time->getTime($localMessageFresh);
+		$localMessageFresh = LocalMessage::fromParams($localMessageFresh);
+		$localMessageReturned = $this->localMessageData;
+		$localMessageReturned['id'] = 1;
+		$localMessageReturned['recipients'] = [['email' => 'use2@testing.com', 'label' => 'User Two']];
+		$localMessageReturned['sendAt'] = $this->time->getTime();
+		$localMessageReturned = LocalMessage::fromParams($localMessageReturned);
+		// define attachment service returns
+		$this->outboxService->expects($this->once())->method('saveMessage')
+			->with(
+				$this->localAccount,
+				$localMessageFresh,
+				[['email' => 'user2@testing.com', 'label' => 'User Two']],
+				[],
+				[],
+				[$localAttachmentReturned->jsonSerialize()]
+			)->willReturn($localMessageReturned);
+		$this->outboxService->expects($this->once())->method('sendMessage')
+			->with(
+				$localMessageReturned,
+				$this->localAccount,
+			)->willReturn($localMessageReturned);
+		// construct mail provider message with attachment
+		$mailMessage = $this->mailMessage;
+		$mailMessage->setAttachments($this->mailAttachment);
+		// test send message
+		$this->commandSend->perform('user1', '100', $mailMessage);
+	}
+
+	public function testPerformWithOutAttachment(): void {
+		// define time factory return
+		$this->time->method('getTime')->willReturn(1719792000);
+		// define account service returns
+		$this->accountService->method('find')->will(
+			$this->returnValueMap([
+				['user1', 100, $this->localAccount]
+			])
+		);
+		// construct mail app message objects
+		$localMessageFresh = $this->localMessageData;
+		$localMessageFresh['sendAt'] = $this->time->getTime($localMessageFresh);
+		$localMessageFresh = LocalMessage::fromParams($localMessageFresh);
+		$localMessageReturned = $this->localMessageData;
+		$localMessageReturned['id'] = 1;
+		$localMessageReturned['recipients'] = [['email' => 'use2@testing.com', 'label' => 'User Two']];
+		$localMessageReturned['sendAt'] = $this->time->getTime();
+		$localMessageReturned = LocalMessage::fromParams($localMessageReturned);
+		// define attachment service returns
+		$this->outboxService->expects($this->once())->method('saveMessage')
+			->with(
+				$this->localAccount,
+				$localMessageFresh,
+				[['email' => 'user2@testing.com', 'label' => 'User Two']],
+				[],
+				[],
+				[]
+			)->willReturn($localMessageReturned);
+		$this->outboxService->expects($this->once())->method('sendMessage')
+			->with(
+				$localMessageReturned,
+				$this->localAccount,
+			)->willReturn($localMessageReturned);
+		// construct mail provider message
+		$mailMessage = $this->mailMessage;
+		// test send message
+		$this->commandSend->perform('user1', '100', $mailMessage);
+	}
+
+	public function testPerformWithInvalidAttachment(): void {
+		// construct mail provider message with attachment
+		$mailMessage = $this->mailMessage;
+		$mailMessage->setAttachments(new Attachment('This is the contents of our plan', 'plan.txt', ''));
+		// define exception condition
+		$this->expectException(SendException::class);
+		// test send message
+		$this->commandSend->perform('user1', '100', $mailMessage);
+	}
+
+	public function testPerformWithInvalidTo(): void {
+		// construct mail provider message
+		$mailMessage = $this->mailMessage;
+		$mailMessage->setTo(new Address('', 'User Two'));
+		// define exception condition
+		$this->expectException(SendException::class);
+		$this->expectExceptionMessage('Invalid Message Parameter: All TO, CC and BCC addresses MUST contain at least an email address');
+		// test send message
+		$this->commandSend->perform('user1', '100', $mailMessage);
+	}
+
+	public function testPerformWithInvalidCc(): void {
+		// construct mail provider message
+		$mailMessage = $this->mailMessage;
+		$mailMessage->setCc(new Address('', 'User Three'));
+		// define exception condition
+		$this->expectException(SendException::class);
+		$this->expectExceptionMessage('Invalid Message Parameter: All TO, CC and BCC addresses MUST contain at least an email address');
+		// test send message
+		$this->commandSend->perform('user1', '100', $mailMessage);
+	}
+
+	public function testPerformWithInvalidBcc(): void {
+		// construct mail provider message
+		$mailMessage = $this->mailMessage;
+		$mailMessage->setBcc(new Address('', 'User Three'));
+		// define exception condition
+		$this->expectException(SendException::class);
+		$this->expectExceptionMessage('Invalid Message Parameter: All TO, CC and BCC addresses MUST contain at least an email address');
+		// test send message
+		$this->commandSend->perform('user1', '100', $mailMessage);
+	}
+
+	public function testPerformWithAccountServiceFailure(): void {
+		// define time factory return
+		$this->time->method('getTime')->willReturn(1719792000);
+		// define account service returns
+		$this->accountService->method('find')->will(
+			$this->throwException(new ClientException('Something went wrong'))
+		);
+		
+		// construct mail provider message
+		$mailMessage = $this->mailMessage;
+		// define exception condition
+		$this->expectException(SendException::class);
+		$this->expectExceptionMessage('Error: occurred while retrieving mail account details');
+		// test send message
+		$this->commandSend->perform('user1', '100', $mailMessage);
+	}
+
+	public function testPerformWithAttachmentServiceFailure(): void {
+		// define time factory return
+		$this->time->method('getTime')->willReturn(1719792000);
+		// define account service returns
+		$this->accountService->method('find')->will(
+			$this->returnValueMap([
+				['user1', 100, $this->localAccount]
+			])
+		);
+		// define attachment service returns
+		$this->attachmentService->expects($this->once())->method('addFileFromString')
+			->with(
+				'user1',
+				$this->mailAttachment->getName(),
+				$this->mailAttachment->getType(),
+				$this->mailAttachment->getContents()
+			)->will(
+				$this->throwException(new UploadException('Something went wrong'))
+			);
+		// construct mail provider message with attachment
+		$mailMessage = $this->mailMessage;
+		$mailMessage->setAttachments($this->mailAttachment);
+		// define exception condition
+		$this->expectException(SendException::class);
+		$this->expectExceptionMessage('Error: occurred while saving mail message attachment');
+		// test send message
+		$this->commandSend->perform('user1', '100', $mailMessage);
+	}
+
+	public function testPerformWithOutboxServiceSendFailure(): void {
+		// define time factory return
+		$this->time->method('getTime')->willReturn(1719792000);
+		// define account service returns
+		$this->accountService->method('find')->will(
+			$this->returnValueMap([
+				['user1', 100, $this->localAccount]
+			])
+		);
+		// construct mail app message objects
+		$localMessageFresh = $this->localMessageData;
+		$localMessageFresh['sendAt'] = $this->time->getTime($localMessageFresh);
+		$localMessageFresh = LocalMessage::fromParams($localMessageFresh);
+		$localMessageReturned = $this->localMessageData;
+		$localMessageReturned['id'] = 1;
+		$localMessageReturned['recipients'] = [['email' => 'use2@testing.com', 'label' => 'User Two']];
+		$localMessageReturned['sendAt'] = $this->time->getTime();
+		$localMessageReturned = LocalMessage::fromParams($localMessageReturned);
+		// define outbox service returns
+		$this->outboxService->expects($this->once())->method('saveMessage')
+			->with(
+				$this->localAccount,
+				$localMessageFresh,
+				[['email' => 'user2@testing.com', 'label' => 'User Two']],
+				[],
+				[],
+				[]
+			)->willReturn($localMessageReturned);
+		$this->outboxService->expects($this->once())->method('sendMessage')
+			->with(
+				$localMessageReturned,
+				$this->localAccount,
+			)->will(
+				$this->throwException(new \Exception('Something went wrong'))
+			);
+		// construct mail provider message
+		$mailMessage = $this->mailMessage;
+		// define exception condition
+		$this->expectException(SendException::class);
+		$this->expectExceptionMessage('Error: occurred while sending mail message');
+		// test send message
+		$this->commandSend->perform('user1', '100', $mailMessage);
+	}
+}
diff --git a/tests/Unit/Provider/MailProviderTest.php b/tests/Unit/Provider/MailProviderTest.php
new file mode 100644
index 0000000000..dd8ba23fb9
--- /dev/null
+++ b/tests/Unit/Provider/MailProviderTest.php
@@ -0,0 +1,218 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * SPDX-FileCopyrightText: 2024 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+namespace OCA\Mail\Tests\Unit\Provider;
+
+use ChristophWurst\Nextcloud\Testing\TestCase;
+use OCA\Mail\Account;
+use OCA\Mail\Db\MailAccount;
+use OCA\Mail\Exception\ClientException;
+use OCA\Mail\Provider\MailProvider;
+use OCA\Mail\Provider\MailService;
+use OCA\Mail\Service\AccountService;
+use OCP\IL10N;
+use OCP\Mail\Provider\Address as MailAddress;
+use PHPUnit\Framework\MockObject\MockObject;
+use Psr\Container\ContainerInterface;
+use Psr\Log\LoggerInterface;
+use Psr\Log\NullLogger;
+
+class MailProviderTest extends TestCase {
+
+	private ContainerInterface&MockObject $containerInterface;
+	private AccountService&MockObject $accountService;
+	private LoggerInterface $logger;
+	private IL10N&MockObject $l10n;
+
+	protected function setUp(): void {
+		parent::setUp();
+
+		$this->containerInterface = $this->createMock(ContainerInterface::class);
+		$this->accountService = $this->createMock(AccountService::class);
+		$this->logger = new NullLogger();
+		$this->l10n = $this->createMock(IL10N::class);
+
+	}
+
+	public function testId(): void {
+
+		// construct mail provider
+		$mailProvider = new MailProvider($this->containerInterface, $this->accountService, $this->logger, $this->l10n);
+		// test set by constructor
+		$this->assertEquals('mail-application', $mailProvider->id());
+
+	}
+
+	public function testLabel(): void {
+		
+		// define l10n return
+		$this->l10n->expects(self::once())->method('t')->willReturn('Mail Application');
+		// construct mail provider
+		$mailProvider = new MailProvider($this->containerInterface, $this->accountService, $this->logger, $this->l10n);
+		// test set by constructor
+		$this->assertEquals('Mail Application', $mailProvider->label());
+
+	}
+
+	public function testHasServices(): void {
+		
+		// construct dummy mail account
+		$mailAccount = new Account(new MailAccount([
+			'accountId' => 100,
+			'accountName' => 'User One',
+			'emailAddress' => 'user1@testing.com',
+			'imapHost' => '',
+			'imapPort' => '',
+			'imapSslMode' => false,
+			'imapUser' => '',
+			'smtpHost' => '',
+			'smtpPort' => '',
+			'smtpSslMode' => false,
+			'smtpUser' => '',
+		]));
+		// define account services find
+		$this->accountService->expects($this->any())->method('findByUserId')
+			->will(
+				$this->returnValueMap([
+					['user0', []],
+					['user1', [100 => $mailAccount]]
+				])
+			);
+		// construct mail provider
+		$mailProvider = new MailProvider($this->containerInterface, $this->accountService, $this->logger, $this->l10n);
+		// test result with no services found
+		$this->assertFalse($mailProvider->hasServices('user0'));
+		// test result with services found
+		$this->assertTrue($mailProvider->hasServices('user1'));
+
+	}
+
+	public function testListServices(): void {
+		
+		// construct dummy mail account
+		$mailAccount = new Account(new MailAccount([
+			'accountId' => 100,
+			'accountName' => 'User One',
+			'emailAddress' => 'user1@testing.com',
+			'imapHost' => '',
+			'imapPort' => '',
+			'imapSslMode' => false,
+			'imapUser' => '',
+			'smtpHost' => '',
+			'smtpPort' => '',
+			'smtpSslMode' => false,
+			'smtpUser' => '',
+		]));
+		// construct dummy mail service
+		$mailService = new MailService(
+			$this->containerInterface,
+			'user1',
+			'100',
+			'User One',
+			new MailAddress('user1@testing.com', 'User One')
+		);
+		// define account services find
+		$this->accountService->expects($this->any())->method('findByUserId')
+			->will(
+				$this->returnValueMap([
+					['user0', []],
+					['user1', [$mailAccount]]
+				])
+			);
+		// construct mail provider
+		$mailProvider = new MailProvider($this->containerInterface, $this->accountService, $this->logger, $this->l10n);
+		// test result with no services found
+		$this->assertEquals([], $mailProvider->listServices('user0'));
+		// test result with services found
+		$this->assertEquals([100 => $mailService], $mailProvider->listServices('user1'));
+
+	}
+
+	public function testFindServiceById(): void {
+		
+		// construct dummy mail account
+		$mailAccount = new Account(new MailAccount([
+			'accountId' => 100,
+			'accountName' => 'User One',
+			'emailAddress' => 'user1@testing.com',
+			'imapHost' => '',
+			'imapPort' => '',
+			'imapSslMode' => false,
+			'imapUser' => '',
+			'smtpHost' => '',
+			'smtpPort' => '',
+			'smtpSslMode' => false,
+			'smtpUser' => '',
+		]));
+		// construct dummy mail service
+		$mailService = new MailService(
+			$this->containerInterface,
+			'user1',
+			'100',
+			'User One',
+			new MailAddress('user1@testing.com', 'User One')
+		);
+		// define account services find
+		$this->accountService->expects($this->any())->method('find')
+			->willReturnCallback(
+				fn (string $userId, int $serviceId) => match (true) {
+					$userId === 'user1' && $serviceId === 100 => $mailAccount,
+					default => throw new ClientException()
+				}
+			);
+		// construct mail provider
+		$mailProvider = new MailProvider($this->containerInterface, $this->accountService, $this->logger, $this->l10n);
+		// test result with no services found
+		$this->assertEquals(null, $mailProvider->findServiceById('user0', '100'));
+		// test result with services found
+		$this->assertEquals($mailService, $mailProvider->findServiceById('user1', '100'));
+
+	}
+
+	public function testFindServiceByAddress(): void {
+		
+		// construct dummy mail account
+		$mailAccount = new Account(new MailAccount([
+			'accountId' => 100,
+			'accountName' => 'User One',
+			'emailAddress' => 'user1@testing.com',
+			'imapHost' => '',
+			'imapPort' => '',
+			'imapSslMode' => false,
+			'imapUser' => '',
+			'smtpHost' => '',
+			'smtpPort' => '',
+			'smtpSslMode' => false,
+			'smtpUser' => '',
+		]));
+		// construct dummy mail service
+		$mailService = new MailService(
+			$this->containerInterface,
+			'user1',
+			'100',
+			'User One',
+			new MailAddress('user1@testing.com', 'User One')
+		);
+		// define account services find
+		$this->accountService->expects($this->any())->method('findByUserIdAndAddress')
+			->will(
+				$this->returnValueMap([
+					['user0', 'user0@testing.com', []],
+					['user1', 'user1@testing.com', [$mailAccount]]
+				])
+			);
+		// construct mail provider
+		$mailProvider = new MailProvider($this->containerInterface, $this->accountService, $this->logger, $this->l10n);
+		// test result with no services found
+		$this->assertEquals(null, $mailProvider->findServiceByAddress('user0', 'user0@testing.com'));
+		// test result with services found
+		$this->assertEquals($mailService, $mailProvider->findServiceByAddress('user1', 'user1@testing.com'));
+
+	}
+
+}
diff --git a/tests/Unit/Provider/MailServiceTest.php b/tests/Unit/Provider/MailServiceTest.php
new file mode 100644
index 0000000000..301c18556c
--- /dev/null
+++ b/tests/Unit/Provider/MailServiceTest.php
@@ -0,0 +1,90 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * SPDX-FileCopyrightText: 2024 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+namespace OCA\Mail\Tests\Unit\Provider;
+
+use ChristophWurst\Nextcloud\Testing\TestCase;
+use OCA\Mail\Provider\MailService;
+use OCP\Mail\Provider\Address;
+use Psr\Container\ContainerInterface;
+
+class MailServiceTest extends TestCase {
+
+	private MailService $mailService;
+	private Address $primaryAddress;
+
+	protected function setUp(): void {
+		parent::setUp();
+
+		$container = $this->createMock(ContainerInterface::class);
+
+		$this->primaryAddress = new Address('test@testing.com', 'Tester');
+
+		$this->mailService = new MailService(
+			$container,
+			'user1',
+			'service1',
+			'Mail Service',
+			$this->primaryAddress
+		);
+	}
+
+	public function testId(): void {
+		
+		$this->assertEquals('service1', $this->mailService->id());
+
+	}
+
+	public function testCapable(): void {
+		
+		// test matched result
+		$this->assertEquals(true, $this->mailService->capable('MessageSend'));
+
+	}
+
+	public function testCapabilities(): void {
+
+		// test collection result
+		$this->assertEquals([
+			'MessageSend' => true,
+		], $this->mailService->capabilities());
+
+	}
+
+	public function testLabel(): void {
+		
+		// test set by constructor
+		$this->assertEquals('Mail Service', $this->mailService->getLabel());
+		// test set by setter
+		$this->mailService->setLabel('Mail Service 2');
+		$this->assertEquals('Mail Service 2', $this->mailService->getLabel());
+
+	}
+
+	public function testPrimaryAddress(): void {
+		
+		// test set by constructor
+		$this->assertEquals($this->primaryAddress, $this->mailService->getPrimaryAddress());
+		// test set by setter
+		$address = new Address('tester@testing.com');
+		$this->mailService->setPrimaryAddress($address);
+		$this->assertEquals($address, $this->mailService->getPrimaryAddress());
+
+	}
+
+	public function testSecondaryAddresses(): void {
+		
+		// test set by setter
+		$address1 = new Address('test1@testing.com');
+		$address2 = new Address('test2@testing.com');
+		$this->mailService->setSecondaryAddresses($address1, $address2);
+		$this->assertEquals([$address1, $address2], $this->mailService->getSecondaryAddresses());
+
+	}
+
+}