[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:  close         |     Focuses:
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Changes (by SirLouen):

 * keywords:  needs-testing => close


Comment:

 I've found the solution to this problem. After reviewing Sendmail and PHP
 code, I was trying to understand how the Sender processing was being done,
 as it made no sense to me (plus the `sendmail_from` thing). I thought that
 the problem was that it was adding a `sendmail_from` but this was
 irrelevant. It's true that having a `sendmail_from` set up, will set it as
 the Sender envelop but not because of PHP default behaviour but a
 PHPMailer casuistry that is not relevant to this specific problem.

 The thing is that all issues fall into PHPMailer: it was basically double-
 setting the `-f` parameter if the `sendmail_path` was set (as many had,
 and as it is a recommendation by the PHP docs).

 I've already proposed a fix, and I will rush it to have it ready before
 6.9.1 release.

 For those having the issue and want a temporary fix, just set the Sender
 to empty as commented here
 https://core.trac.wordpress.org/ticket/64368#comment:4

 Once updated to 6.9.1 this code can be removed.

 cc @studiomondiale @digitalblanket

 I'm adding `close` as a candidate of `reported-upstream` once this has
 been sorted out.

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Ticket URL: <https://core.trac.wordpress.org/ticket/64368#comment:8>
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