Missing email mystery

11330 pts.
Bounced email
Exchange Server
Microsoft Outlook
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.

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Well, I’m still somewhat puzzled – but have a partial answer today. The client’s contact eventually called me to report that all emails (including the ones I requested) which were blocked had PDF attachments. I asked her to read one of the non-delivery reports to me over the phone, and there was a reference to the size of the attachment….so I will have to go with that. The contact protested that she often sends much larger PDFs, this was a single page which should have passed through without issue (she has previously sent 68 page PDF files without issue) but I’m guessing there was file corruption involved. I could not confirm this, as she was unable to give me a file size…..but that’s where it stands.

Newer PDFs may also have content other than embedded text. There can be executables, web links and other more active content. This could also be blocked by some mechanism along the path. It does seem strange that there is no other information in the NDR’s. Some email filters are not “smart” so try renaming the file attachment to something other than PDF.

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  • petkoa
    Hi AndreaF, Well, you say "no sign of this arriving at the inbox" - is it possible these e-mails are moved directly to the spam folder by the Outlook's Bayesian spam filter? I had experience with some my e-mails containing PDF files and some non-english text to be filtered by this filter... When I forwarded their copies-to-self so the mails got some "original message... forwarded by... lines in the body text, they succesfully passed the filter. And some experience with the Bayesian spam filter of the Mozilla suite - any mails containing just an attachment - image, PDF - and no message text per se, end up in the spam folder (though Mozilla was not so choosy about the message language)... Hope this observations could help, BR, Petko
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