I don't know enough to know if this is relevant. When I did an mxtoolbox check at the time I was configured to use Fastmail, there were a few warnings about DMARC, which I don't think is an issue, but there was this:
smtp - in1-smtp.messagingengine.com - Reverse DNS does not match SMTP Banner
smtp - in1-smtp-messagingengine.com - Warning - Does not support TLS
smtp - in1-smtp-messagingengine.com - 15.578 seconds - Not good! on Transaction time
Is the first warning relevant? I know the second two might not be.
EDIT: Did a little more digging. I wonder if that could be the cause?
https://blog.mxtoolbox.com/2010/03/2...agnostic-tool/
Quote:
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This is only a warning, and in some cases you may have no control over this. However, if you have the ability to make these match, you should. Some mail servers look for this and use it to mark messages you send as questionable. Most mail systems will not reject your messages outright, but this may effect your spam score increasing the likelihood your messages will be marked as spam.
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Keep in mind I was using Fastmail's DNS, the support rep said all the settings were fine, I was sending THROUGH their app using a domain that was set up to work directly through Fastmail.
Now that I've moved to my own email hosting and off Fastmail, I do not see any of these errors... and my email is once again being delivered properly.