We started having some mail go missing a few weeks ago. Had a couple of users report that they were trying to reset passwords at vendor sites and that their password reset email was not arriving. Nothing is ever found with a msg trace and no bounceback’s to the sender. dmarcian reports for our domain come back with 0 issues. What could cause this? Now, as of today we just had a couple more reports of email not arriving and it is not in quarantien and cannot be found with a message trace, so this is becoming very problematic.
Are your mx servers in your DNS settings pointing to one provider. i.e. microsoft mx servers only?