Special header folding when using PHP's mail function still required?

[daeppen]

To my understanding, special handling regarding header folding when using PHPMailer::isMail() (mail()) has been introduced in b25f93e and 21b35dc along with the constant MAIL_MAX_LINE_LENGTH due to #818.
I'm curious if this is still an issue (by the mail() function) in recent PHP versions? Currently I'm unable to reproduce the issue using PHP 8.2.15. Meaning when I set MAIL_MAX_LINE_LENGTH to 998 the headers are not broken.
Is anyone able to reproduce the issue which would still legitimate the existence of MAIL_MAX_LINE_LENGTH?

Background: I'm trying to implement List-Unsubscribe. My tests show that certain mail clients (tested with Thunderbird, FairEmail & eM Client) seem not yet to support folded List-Unsubscribe headers. Dropping MAIL_MAX_LINE_LENGTH or increasing it to 998 prevents folding on List-Unsubscribe in my use cases.

[Synchro]

Indeed I've not been able to repro this issue myself, but "works for me" isn't a great defence! Overall I always recommend using SMTP to localhost instead of using mail(). It's safer, faster, and provides better debug feedback.

With the recent revelation in #3012 that PHP may have changed its policy on line breaks in the mail function, I see even fewer reasons to support it as it makes legacy support increasingly difficult.

[daeppen]

Thanks for your quick reply. I understand. So I'll switch to SMTP for good.

[campbell-m]

If you're thinking of dropping support for mail() then I'm sure you'll appreciate that there are many existing sites using mail() - however inadvisedly - for whom that would be a shock if it were suddenly dropped without some kind of graceful transition path to SMTP.

[Synchro]

Oh, I'm not thinking of dropping it, but I will keep recommending not using it!

[campbell-m]

OK!