There seems to be a file association problem with Firefox on at least Windows XP Pro in my environment. Firefox seems to associate DOC files with application/applefile (which makes no sense), which makes it impossible for some emails to make it through certain scans (Content-Type to extension comparisons). I've been able to replicate the issue on FF 3.0.3 and 126.96.36.199 on Windows XP Pro in multiple environments with MS Office 2007 installed.
Emails with DOC files attached in these environments receive the following:
Content-Type: application/applefile; name="Test Doc.doc"
Content-Disposition: attachment; filename="Test Doc.doc"
I can't seem to get Firefox to switch from application/applefile to application/msword. If the same attachments are attached via IE 7 environments, they are attached with the correct content types of application/msword. I've posted on Mozilla's forums for ideas.
When MS Word 2007 or any other MS Office product isn't installed, DOC files are attached at an octet-stream:
Content-Type: application/octet-stream; name="Test Doc.doc"
NOTE: Could not replicate on a Vista x64 Ultimate machine running FF 3.0.3 with MS Office 2007.