A few of my users have been getting this error message recently:
Code:
VIRUS ALERT

Our content checker found
    virus: Encrypted.Zip

in an email to you from unknown sender:
  ?@XXXXXXX
claiming to be: <XXXXXXXXX>

Content type: Virus
Our internal reference code for your message is 13680-01/S62Cm+YbRe-7

First upstream SMTP client IP address: [XXXXXXX] XXXXXXXXXX
According to a 'Received:' trace, the message originated at:
[XXXXXXXX],
  XXXXXXXXX [XXXXXXXXXXX]
What is the best way to allow encrypted zip files to pass through?

Thanks