[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:  needs-patch   |     Focuses:
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Comment (by SirLouen):

 Replying to [comment:78 jorbin]:
 > Because this is a regression that can fully break outbound email, that
 damaged IP reputation can hurt not just one site or application, and that
 reverting it (or downgrading to 6.8.3) has successfully solved the issue
 for every reporter, I think that the safest route for 6.9.1 is to revert
 [61010] rather than upgrade phpmailer. This doesn't need to preclude work
 in 7.0 that builds upon this attemmpt and tries to find new ways to ensure
 emails are successfully delivered.

 With those premises, this is completely untestable. Precisely, things like
 RC here are completely useless because no one uses them anywhere near
 production (reason why no one caught this simple issue, which was
 theoretically "affecting deliverability").

 The same is going to happen again here: no “reporter” is going to test any
 move towards 7.0. As Johnatan said, there was not enough critical mass to
 consider that this regression was urgent for a prompt 6.9.1 release for a
 reason is apparently impacting only a little subset of users with not
 ideally configured hosts according to hosting good practices.

 We have reproduced the same conditions that they reported both manually
 and with unit tests: PHPMailer was simply bypassing the user-set (hosting-
 set) configuration in `php.ini`. With the PHPMailer patch, it will not be
 bypassed anymore and respect the user configs. What @siliconforks
 reproduced was accurately the affecting problem: PHPMailer is not
 overriding `php.ini` any more.

 @siliconforks said:
 > Then I tried sending mail again using the Health Check plugin. This time
 I received the dreaded error message "Could not instantiate mail
 function".

 As simple as this.

 I not going to start a workflow keyword war. Do whatever you like.

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Ticket URL: <https://core.trac.wordpress.org/ticket/64368#comment:80>
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