[wp-trac] [WordPress Trac] #64368: `Could not instantiate mail function` errors sending mail in 6.9

[WordPress Trac]

#64368: `Could not instantiate mail function` errors sending mail in 6.9
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 Reporter:  desrosj       |       Owner:  SirLouen
     Type:  defect (bug)  |      Status:  accepted
 Priority:  normal        |   Milestone:  6.9.1
Component:  Mail          |     Version:  6.9
 Severity:  normal        |  Resolution:
 Keywords:  has-patch     |     Focuses:
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Comment (by SirLouen):

 Replying to [comment:57 siliconforks]:
 > Huh?  Isn't SPF always a concern?  (Did you read my
 [https://core.trac.wordpress.org/ticket/64368#comment:48 comment above]?)

 Maybe those are working inboxes for some reason.

 But still, I can't really understand why anyone would prefer to sacrifice
 DMARC passing in exchange of return-path address validity.

 > The issue I’m raising is specifically about recipient-side anti-spam
 behaviour and RFC compliance. Many anti-spam systems evaluate whether the
 envelope sender corresponds to a valid mailbox and factor invalid return
 paths into their scoring or reputation calculations over time (for example
 when bounces cannot be delivered because the mailbox does not exist).

 Obviously every element matters, and there was also a proposal to do quick
 validity checks for inboxes in Health Check in #62129

 But still, if we are seriously concerned about deliverability at mass
 scale, owning the domain and setting it up correctly (not only the SPF,
 but DKIM and FQDN alignment) are like the bare basics. Following the 80%
 rule, satisfying most of the population, having a From = Sender is the
 most popular option (this was the purpose of returning this feature
 despite of the minor troubles we have found with PHPMailer).

 For the rest, there are many tweaking options that, as I commented in
 #60420, anyone with expertise willing to go the extra mile to finetune the
 thing should know. We should not sacrifice the majority in exchange of
 some special needs.
 [https://core.trac.wordpress.org/ticket/64368?replyto=57#comment As I have
 demonstrated here], in a cheap, classic webhost, maximum deliverability is
 truly simple (and personally I rarely work with regular webhosts, but I'm
 conscious that the majority does).

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Ticket URL: <https://core.trac.wordpress.org/ticket/64368#comment:58>
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