Found the problem!  I had a trailing comma in the Clamwall banned extension list which apparently tells Clamwall to ban any file without an extension.  Removing the comma allows files without extensions to pass.

I just had a message quarantined as banned extensions but I don't understand why.  The message contained three jpeg images named "AQseven", "FooterSignature", and "AQLogin".  No extensions to these filenames.  Can anyone explain why this message was quarantined as having banned extension?

Clamwall is configured with the following banned extensions: PIF,LNK,SCR,VBS,BAT,COM,EXE,CMD,EML,CPL,VBE,WBT,WSH

Seems strange but check the Clamwall log and see if there is any clue there.

Nothing enlightening in the clamwall log.  Just the expected entries of:

B 20150729 103746.116 MG0013F2 AQseven, FooterSignature, AQLogin
K 20150729 103746.116 MG0013F2 Killed!