[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 has-unit-tests  |     Focuses:
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Comment (by desrosj):

 I just wanted to share another data point that I came across today.

 I organize a local WP meetup and I had someone reach out to me asking if
 I'd received the topic they submitted through the apply to speak form on
 the website. After confirming where that email is supposed to go, I
 checked and no email was ever received (checked spam as well).

 I had to reset my password to log into the site, but I was also not
 receiving password reset emails from WordPress itself. I spent about 10
 minutes trying to get some type of error message but was unable to. After
 changing the from email to one that exists on the same domain as the site,
 the emails started working again without issue.

 I suspect that the emails were not sending due to this issue because they
 were working in October/November, but I can't yet confirm it as I'm not
 100% certain. But it's a good example because I only discovered that
 emails were broken when someone reached out to me to follow up. I'll try
 to find some time this week to figure out the root cause and confirm that
 emails worked on the site as previously configured on 6.8.x or with
 [61010] reverted.

 I agree with reverting the original change for 6.9.1. To be clear, I held
 this opinion before I discovered this issue on my meetup's site. But
 wanted to offer another site's situation for consideration.

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Ticket URL: <https://core.trac.wordpress.org/ticket/64368#comment:86>
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