bug#46323 [Mailer] SMTP transport does not provide the (final) Message-ID

Questions / Answers:

• Q: Why storing 250 inside$mtaResult instead of using the already available$message->getDebug()?
• A: Because the later may be huge (especially in case of attachment) and running a regexp over it would be less than safe. Instead$mtaResult only contains one line
• Q: Why a newpublic method?
• A: Because child SMTP Transport may make other assumptions about the return250 Ok value and provide a custom logic / regexp.
• Q: Whyregexp?
• A: Because there is no official standard for this line (other than the250 Ok prefix)

Additionally (seehttps://symfony.com/releases):

• Always add tests and ensure they pass.I can't. Don't have the time. Left to maintainers / other contributors
• Bug fixes must be submitted against the lowest maintained branch where they apply (lowest branches are regularly merged to upper ones so they get the fixes too.)
• Features and deprecations must be submitted against the latest branch.
• Changelog entry should followhttps://symfony.com/doc/current/contributing/code/conventions.html#writing-a-changelog-entry
• Never break backward compatibility (seehttps://symfony.com/bc).