Symfony version(s) affected: 4.4.1

Description

When only one email is sent in a Symfony application having also the Messenger component, two MessageEvents are actually dispatched.
Not sure if it is a bug or it is done on purpose, but it brings some confusion in the Web profiler where it shows a queued email in a "[main]" transport :

Seen also in functional tests using non-mocked, by default injected dependencies and checking sent emails count through dispatched events.

How to reproduce

In a Symfony 4.4 application in development mode (web profiler and debug activated), having Messenger component, and an implemented Mailer.
When an email is sent and Mailer is configured for 1 dsn, it should show 2 emails in web profiler, one sent by the actual configured dsn, and one queued in a "[main]" transport.

Possible Solution
Remove the MessageEvent dispatch inSymfony\Component\Mailer\Mailer:send and keep only the Messenger's MessageBus dispatch.

Additional context
The 2 MessageEvents come from :

• dispatched inSymfony\Component\Mailer\Transport\AbstractTransport:send
• inSymfony\Component\Mailer\Mailer:send - if MessageBus is not null (the dispatched transport in MessageEvent is an instance ofSymfony\Component\Mailer\Transport\Transports)