I'm trying to find possible places to look for an issue that I'm struggling with on my website. Scenario:
Ubuntu server uses sendmail and configured mail relay to go through our O365 servers. This was working on all environments 2 weeks ago, then stopped working on production only. To: is submitted to firstname.lastname@example.org and is also CC: to email@example.com. The gmail.com contact form submissions come through without problems, but the example.com mailbox never receives the messages. IF, however, I send a test message from the web server to the example.com email address it is received in the mailbox.
It seemed odd to me that only one of the accounts are receiving the form, so I talked to my email admin and he's seeing the same consistency as the mailbox (so it doesn't appear to be a user issue on the mailbox).
At this point, it would all seem to point to the application configuration (WP) or a variation in the code or DB causing the issue - right? However, as one of the first steps in trying to resolve the issue, I did a backup from staging server (where the emails are working fine) and staging DB to push said snapshot into production (with literally the only thing changing in the process was a bulk-edit of the URL in the DB script).
What am I missing?