[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 dmsnell):

 > A Site Health notice like:
 >
 > “Your domain does not publish SPF, DKIM, or DMARC records. Emails sent
 from this site are likely to be rejected or spam-foldered.”

 For some time I’ve been chatting with folks about the idea of a new panel
 in `wp-admin` for “Web Standards” support and this is exactly one of the
 things I’d like to see added there. Unfortunately I’m unable to add it
 myself because I’m already fully occupied with other work.

 In the meantime, plugins can fulfill that purpose, but I’d love to see
 some work to build a design for how this could serve everyone in Core:
 email settings, `.well-known` directory paths, RSS/Atom/ActivityPub
 integrations, web server settings, and more.

 > decision to always define an Envelope-From address

 @Monarobase can you help me understand this, because it was my
 understanding that WordPress was already sending out an `Envelope-From`
 address before this change. Here are a couple of test emails sent while I
 was trying to confirm the patch.

  - [https://aboutmy.email/200fda9e/session before the patch was applied]
 [[br]]`MAIL FROM:<exouser at image-build-instance-
 ubuntu-24-1761002402583201839.js2local>`
  - [https://aboutmy.email/a9f9d1e/session after the patch was applied]
 [[br]]`MAIL FROM:<wordpress at 149.165.153.253>`

 This was for a vanilla installation of WordPress on a fresh Ubuntu node.
 Maybe you are saying that WordPress did not send anything through
 `PHPMailer` in the //before// case, and PHP’s `mail()` auto-set it? and
 somehow that would be some default that hosts configure in a way that it
 would be valid? For reference, the auto-generated value here (before the
 patch was applied) was the Linux user on the server running `nginx` @ the
 local hostname and domain name, something as far as I can tell is
 unavailable for discovery publicly.

 Have to admit the details here confuse me, and I’m leaning on everyone
 else’s expertise. If you can help us understand how to see what you are
 seeing between the call to `mail()` and the MTAs I would personally value
 that.

 Specifically, before this patch, my emails were sending with an invalid
 mailbox; yet, you are pointing out that this patch //created// the problem
 of sending from an invalid mailbox. That’s what I’m currently struggling
 to understand.

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Ticket URL: <https://core.trac.wordpress.org/ticket/64368#comment:47>
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