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Vote for XWall for Microsoft Exchange
The XWall is a server based spam filter that works. It's that simple. Ask anybody or try it yourself. XWall for Microsoft Exchange (5.5, 2000, 2003, 2007, 2010 including SB versions 32/64bit) and standard SMTP mail servers offers a wide variety of filters to combat spam, junk mail, email viruses, dangerous attachments and many other undesired email situations. XWall may attach disclaimers to outgoing email, and can archive all in and outgoing email. XWall keeps a detailed daily log including several informative statistics.
XWall works with Microsoft Server NT4, 2000, 2003, 2008 Standard, Enterprise and Small Business. It also can be placed on a MS Home server, 2000 Pro, XP or Vista workstation. Microsoft may limit the number of connections on some workstation OS. XWall is available in 32 and 64 bit versions.