[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):

 The reason we consider SPF not to be the concern here is that SPF
 configuration has always been part of email delivery, and most hosting
 providers already handle this today. When domains are hosted with us, SPF
 is preconfigured; when they are not, customers are generally advised to
 copy or adapt existing DNS records. In other words, this change doesn’t
 materially alter the SPF situation.

 From the perspective of an individual website, having From = Sender
 alignment can indeed improve short-term deliverability, and I agree with
 that. However, from a hosting provider’s perspective, there is a different
 — and equally important — consideration: IP reputation.

 Allowing emails to be sent with invalid, non-RFC-compliant return paths
 leads to poorer hygiene at the IP level. Recipient anti-spam systems
 factor this in over time, especially when bounces cannot be delivered
 because the return-path mailbox does not exist. While this may not cause
 immediate failures, it does negatively affect the reputation of the
 sending IP.

 So while I agree this change may improve deliverability in the short term
 for many individual sites, in the medium to long term it risks reducing
 overall deliverability by degrading hosting providers’ IP reputation.

 Today, the only way to achieve maximum deliverability without that trade-
 off is for customers to either:

 - ensure the wordpress at domain.tld mailbox actually exists, or
 - explicitly configure the sender via a plugin or custom code.

 Our concern is simply that the current default optimises for short-term
 gains while introducing longer-term risks at the infrastructure level. We
 hope those longer-term implications can be taken into account, not just
 the immediate improvements.

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Ticket URL: <https://core.trac.wordpress.org/ticket/64368#comment:59>
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