[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):

 All, thank you for continuing to keep up the pace of investigation and
 working to resolve ambiguity, disagreement, and mutual understanding. This
 conversation has, unfortunately, veered far from the purpose of this
 ticket and itself is much broader in scope. Therefore I have created
 #64420 to discuss how WordPress and hosts should broadly interact with the
 Envelope Return-Path.

 For this specific ticket I ask the following:
  - Let’s limit continued discussion exclusively to the `Could not
 instantiate mail function` issue which arose in 6.9 and which has multiple
 existing workarounds available today as well as fixes in the pipeline for
 6.9.1.

 For #64420 I have further asks:
  - Let’s be gracious with each other and trust that we’re all competent
 folks who want to see reliable email deliverability, that we have all
 performed due diligence, and that we might all see different aspects of
 the same root problem. We see different parts of the problem and have
 different ideas on how to resolve them, but email systems //are//
 complicated and hit different cogs of the system in different ways.
  - The //facts// highlighted here have been extremely helpful and build
 shared understanding of how best to move forward. Let’s continue to share
 how different aspects of sending and delivering emails his our own
 systems. //Because// this is such a complicated field and so swamped by
 outdated or uninformed content around the web (sadly, a web search on how
 best to send email is not likely to return accurate, updated, and
 trustworthy information), let’s focus as much as we can on facts we have
 measured. It’s very likely that one large system is doing things
 differently than others.
  - In many of the comments here’s it’s the side-details that have helped
 me most to understand the needs. Let’s continue to share the context and
 assumptions we bring into the discussion. I think there are likely a few
 different overlapping issues at the root of this conversation, including
 things from the perspective of the sender, of the host, of WordPress, of
 the recipients, of middle-man MTAs, of email clients, and more.

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Ticket URL: <https://core.trac.wordpress.org/ticket/64368#comment:68>
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