Civi 4.7.20 / WP 4.8
For the past several weeks, we've been unable to send out any emails or test mails through CiviMail. No errors are logged, and even with backtrace displayed and error debugging enabled, there's no indication of any error. Yet every time we submit a mailing, every recipient email address bounces and is switched to On Hold. The There are no messages in the bounce email inbox (it's a conventional address, same domain name as the website), so it seems those emails never went out from the mail server.
Sending test email in System Settings / Outbound Email / SMTP succeeds, so we know the outbound email settings are correct.
Someone suggested the problem may be VERP is no longer supported on the mail server, so I contacted the hosting provider. I now know for certain that VERP was deprecated, and worse yet, catch-all email accounts are not permitted for shared hosting accounts.
In my limited understanding of CiviMail mechanics, I think we're supposed to either have VERP support or a catch-all email account. But we have neither. Is there a work-around?
Any ideas?
ADDENDUM:
Though we're also experiencing buggy behavior in Reports, I did manage to coax Bounce Reasons out of our system. Syntax errors seem to be the culprit, and they all look like "Failed to add recipient: {email address redacted} [SMTP: Invalid response code received from SMTP server while sending email. This is often caused by a misconfiguration in Outbound Email settings. Please verify the settings at Administer CiviCRM >> Global Setting
"
Also, per Chris' suggestion below, I looked at the "Track replies using VERP" option, and discovered it's already deselected. So while my original question was Can't send or test mail, neither VERP nor catch-all supported, I am changing it to Can't send or test bulk mail, but test mail succeeds in System Settings / Outbound email / SMTP.