Exchange 2010 - This attachment was removed.

recently I've encountered a problem where .pdf attachments were being stripped for particular sender emails.

I had had no .pdf file name, file extension or MIME type listed in my Attachment Filtering Agent so it was a mystery.
You can check the config with command on the edge server:

  • Get-AttachmentFilterEntry |fl
You can also disable Attachment Filtering Agent for testing purposes using following command:
Disable-TransportAgent -Identity "Attachment Filtering agent"

After you confirmed that the problem is due to this agent you can re-enable it:
Enable-TransportAgent -Identity "Attachment Filtering agent"

At this point it was clear that Attachment Filtering Agent was stripping those particular .pdf files created by that specific sender and letting all other .pdf attachments through.

After posting my problem on technet forums it appears that for some reason Attachment Filtering Agent was recognizing those .pdf files as "invalid attachment".

To workaround this you have to do the following:

1.Stop the Microsoft Exchange Transport service.
2.Locate the EdgeTransport.exe.config file. This file is located in the following path: drive:\Program Files\Microsoft\Exchange Server\Bin\
3.Add the following entry between the element and the element of the EdgeTransport.exe.config file
4.Restart the Microsoft Exchange Transport service