cogdog on "[Plugin: Jetpack by WordPress.com] Post By Email Fails to Attach MP3"

A site I built that allows participants to email content regularly generates error messages on attached mp3 files, e,g,

Some attachments were rejected from the following WordPress.com Post by Email:

 - Nimis Kahpimotate Presentation part 2.mp3 - Invalid file type

Although .mp3 is supposed to be a valid upload type (I can upload mp3 via Media Library). It is no a file size issue, we have max uploads set to 100Mb and these are less than 20.

Also, the error message does not help much because it does not give a link to the post so I can fix it.

http://wordpress.org/plugins/jetpack/