[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 Monarobase):

 Thanks for answer. Just to be clear, I wasn’t referring to SPF here — I
 agree it isn’t the concern for this change.

 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).

 Web hosts that block outgoing e-mail that has an invalid return path do so
 to protect their IP reputation.

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Ticket URL: <https://core.trac.wordpress.org/ticket/64368#comment:56>
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