Steps to reproduce

1. Write an email
2. Click send
3. An error, from the backend, is not properly handled

Expected behavior

As a User, I expected a hint/warning when something went wrong.

Actual behavior

Nothing.

To do

• Remove dead code
• Show a warning when the backend operation failed

Additional info

• NoSentMailboxConfiguredError and ManyRecipientsError are mapped from the backend exceptions¹, but the backend does not throw SentMailboxNotSetException and ManyRecipientsException anymore.
• The phpdoc for IMailTransmission.sendMessage is outdated.
• NewMessageModal.onSend may put a draft into the outbox without having a draft saved already (1), update a message in the outbox (2), update an existing draft and put it into the outbox (3).

To simulate a failure for case 1 or 3:

Index: lib/Controller/OutboxController.php
IDEA additional info:
Subsystem: com.intellij.openapi.diff.impl.patch.CharsetEP
< >UTF-8
===================================================================
diff --git a/lib/Controller/OutboxController.php b/lib/Controller/OutboxController.php
--- a/lib/Controller/OutboxController.php	(revision 2cfa6995f9de4d356a28e32c4f12ccf74a679717)
    b/lib/Controller/OutboxController.php	(date 1720696979685)
@@ -145,6  145,8 @@
		// Locate the account to check authorization
		$this->accountService->find($this->userId, $draftMessage->getAccountId());

 		throw new ClientException('Computer says no');
 
		$outboxMessage = $this->service->convertDraft($draftMessage, $sendAt);

		return JsonResponse::success(

There's no feedback that something went wrong, I'm just taking back to the composer, and it says, "Draft saved".