[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:63 Monarobase]:
 > We are not just thinking from a WordPress perspective, we are thinking
 for all of our customers. Should non WordPress users be impacted because
 the people who decide about allowing a new field in the admin interface
 don't consider fixing e-mail deliverability issues is important to them ?

 But this goes beyond this change. Also I need to get a better picture of
 that specific statements regarding "invalid return-path". Because its not
 invalid but not existing. Can you provide us with more literature
 regarding this issue? FWIW, this was a 2000s issue that pretty much almost
 no one cares anymore unless I've missing something more updated (and even
 though, there are plenty of easy fixes, like the ones I commented you,
 including the catch-all option).

 For example, if you send an email, to an invalid address and the remote
 server bounces back to the `Return-Path` which happens also to be invalid,
 being "tagged" as invalid "Return-Path" not necessarily increases any spam
 score nor the IP reputation as you say. Which is the exact system that
 triggers this?

 Definitely not SpamAssassin or derivatives.

 What massively destroys the IP reputation is to mass send emails to
 nonexistent inboxes.

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Ticket URL: <https://core.trac.wordpress.org/ticket/64368#comment:64>
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