My users are complaining because their email messages say the Firebox removed a file called winmail.dat. No-one is sending them files with that name.
This is a pretty common issue with older version of firmware and a knowledge base article, below, was release regarding the most common cause of this behavior and how to address it.
Why do email attachments sent through the SMTP-proxy appear as Winmail.dat attachments?https://watchguardsupport.secure.force.com/publicKB?type=KBArticle&SFDCID=kA2A00000000FnKKAU&lang=en_US
Eugene Torre | Support Engineer