I'm having a problem with digital signatures. I just installed a digital certificate for one of my users and whenever they send a digitally signed email, the recipient recieves the message as a winmail.dat. I verified that it's getting converted/corrupted into winwail.dat before it leaves our gateway, and it's not the mail client because I tried a machine with Office XP and another with Office 2007. No matter who I send the digitally signed message to, it ends up as a winmail.dat for the recipient. Additionally, the message is NOT rich text. This occurs whether the message is sent as plain text, HTML, or rich text.
Windows XP SP3
Office XP & 2007