[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:67 siliconforks]:
 > I think the best discussion of this is probably in RFC 5321 Section 6.2:
 >
 > https://datatracker.ietf.org/doc/html/rfc5321#section-6.2

 There is one single key in that section that explains the whole problem of
 this

 >   To stretch the principle of delivery if possible even further, it may
 be a rational policy to not deliver mail that has an invalid return
 address, although the history of the network is that users are typically
 better served by delivering any message that can be delivered.  Reliably
 determining that a return address is invalid can be a difficult and time-
 consuming process, especially if the putative sending system is not
 directly accessible or does not fully and accurately support VRFY and,
 even if a "drop messages with invalid return addresses" policy is adopted,
 it SHOULD be applied only when there is near-certainty that the return
 addresses are, in fact, invalid.

 RFC acknowledges that determining the validity of a return address is,
 overall, a bad idea and should be applied in very specific scenarios. It
 is not even a requirement but a suggestion. SPF alignment for DMARC is not
 a suggestion.

 Replying to [comment:65 amanandhishoe]:
 > It seems like you are conflating the Reply-To header with the SMTP
 envelope Return-Path. The issue is that WordPress may attempt to influence
 the envelope Return-Path, but that address must be deliverable, since it
 is where mail servers send bounce notifications.

 I was explicitly talking about the Return-Path, not the Reply-To. What
 made you infer that? If at some point it made that impression, I can
 confirm that I was talking exclusively about the Return Path

 > Reputation systems at Gmail, Outlook, Yahoo, and others operate
 independently.

 This reminds me  all the requests regarding Google/Bing Seach engine for
 SEO purposes. WordPress can only stand with "golden rules", not with all
 the theories that help you push up your rankings or like in this case,
 help deliverability based on some "relatively well known rules". As I
 said, Return-Path validity is not a golden rule and as it has been
 commented above, it seems more of a suggestion. But SPF Alignment IS a
 golden rule hands down, and it's explicitely stated in the RFC.

 The worst part, is that system administrators can easily handle Return-
 Path deliverability, knowingly that at least for now, `wordpress at hostname`
 is the default address in WordPress (if they are providing WordPress in
 their service list). But what I call "exemplary users" are completely
 f**** *p if `Sender` address is not present, having to deal with very
 complex hooks and knowledge about PHPMailer to fix their problems.
 WordPress is meant to simplify the life of the exemplary users not the
 system administrators that should have all the tools in the world to make
 things happen.

 [https://core.trac.wordpress.org/ticket/64420#comment:1 Please refer to
 this post], to continue the conversation if needed.

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Ticket URL: <https://core.trac.wordpress.org/ticket/64368#comment:69>
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