SMTP Does Not Authenticate

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Nextcloud version (eg, 20.0.5): 26.0.2
Operating system and version (eg, Ubuntu 20.04): TrueNAS
Apache or nginx version (eg, Apache 2.4.25): replace me
PHP version (eg, 7.4): replace me

The issue you are facing:
SMTP does not work.
I have tried connecting to Google, Yahoo, and Outlook, using SSL, TSL and with no authentication.
In each circumstance, I get this generic error:

A problem occurred while sending the email. Please revise your settings. (Error: Email could not be sent. Check your mail server log)

I have looked through forum posts and articles online, and have not been able to resolve this by any means.

Is this the first time you’ve seen this error? (Y/N): Y

Steps to replicate it:

  1. Attempt to set up SMTP

The main thing that comes to mind to set encryption to None so that STARTTLS will be relied upon by NC to upgrade to whatever encryption is supported by the remote:

You can also turn on mail_smtpdebug to see more details.

If still stuck post your entire config.php redacted - or at least the mail_* parts.

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