I have a client that has begun having issues sending e-mail attachments, which they send a lot of. It seems that this issue started suddenly about 2 weeks ago. The e-mail client settings (smtp server and other account settings) have remained stable for ~3 years, as well as the AV software, which is CA Security Center. As far as I can tell the CA software is not scanning outgoing mail, or at least there is no setting to do so.
Some recipients are receiving a "winmail.dat" attachment instead of the original .pdf or .doc attachment. It seems the affected recipients are those that are not using Outlook as their e-mail client. Can someone tell me what is going on here, and where it is going on at?
I am in the process of changing the SMTP server in our Outlook clients from our ISP (Time Warner cable) to smtpauth.hosting.earthlink.net (our domain host's smtp server), to see if this eliminates the issue.