MAILsweeper for SMTP 4.3 allows remote attackers to bypass virus protection via a mail message with a malformed zip attachment, as exploited by certain MIMAIL virus variants.
https://exchange.xforce.ibmcloud.com/vulnerabilities/13611
http://www.securityfocus.com/bid/8982
http://www.computerworld.co.nz/cw.nsf/0/BF9E8E6E2D313E5FCC256DD70016473F?OpenDocument&More=