One of our clients reported an issue with a contact having email bouncebacks. I looked on the relay server (running ORF with Clamwin) and see the emails in the log - showing as passed through, whitelisted.
When I followed up and spoke with the clients, some said they were receiving these emails with no problems - others did not ever see them in their inbox. I called the sender, and asked for a copy of the error messages, giving them two addresses to send to. One was through our client, the other our own domain - two separate systems, which do not share any email processing.
The address at the client domain shows a record of the email passing through, but - no sign of this arriving at the inbox. Nothing arrived at our company (although I do not work with our own email server, so could not check incoming records).
The only possible issue I can see is an extremely high amount of spam hitting the relay server at our client's location...but I have tested the client's email as well as our own with a variety of outside email addresses....and none had issues with delivery.
I am baffled - any thoughts appreciated.