[Mailer] Added cautionbox for sender

[ThomasLandauer]

TODO: Same for "recipients", line 3141

[javiereguiluz]

The original content might be not great ... but the proposed content doesn't look better in my opinion. It's harder to understand, at least to me.

[ThomasLandauer]

The original "Sender used by the Mailer" is ambiguous, as there are two things called "Sender":

• The Sender: header within the email: https://tools.ietf.org/html/rfc4021#section-2.1.3
• The information used in the SMTP dialogue:

EHLO example.com
MAIL FROM: <me@example.com>
RCPT TO: <you@example.com>
DATA

The latter is sometimes called "envelope sender", but this only makes things worse, since for those who don't know, it's harder to find out what/where this "envelope" lives (correct answer: nowhere ;-) rather than find out what an SMTP session is - see also your #15241 (comment) :-)

So I would suggest to avoid the term "envelope" completely, and even rename the configuration key at https://symfony.com/doc/current/mailer.html#configuring-emails-globally to something like smtp

[javiereguiluz]

Thanks for the provided info Thomas. I've merged and tweaked it a bit to provide more details about which "sender" this is about.

[ThomasLandauer]

@javiereguiluz I can't figure out where I can see what you changed :-( Can you give me a hint?

TODO: Same for "recipients", line 3141

[javiereguiluz]

This is the commit with the changes based on your extended comment: 05e1203

[ThomasLandauer]

Thanks! Doesn't GitHub automatically link them somehow? Can't find "05e1203" on this Conversation page here...