Alternative EMail server for Windows operating systems

Microsoft Exchange is what I and probably most others would recommend without knowing much about your requirements.  If you could provide more information about your requirements then we could provide you alternatives.

Www.pmail.com Mercury Mail.

There are ways to run sendmail, postfix within windows, but the OS overhead and experience suggests using an open source OS on older workstations make many more options available.

Thanks.  I was looking for a packaged Open Source Email Server.

Your requests suggests that the email server must run on window. There are guides on installing/setting up a mail server using Linux.
Mail toaster.etc.

You need to define what functionality you need/want.
Antivirus, anti-spam, AD tie-in? Etc.

Zimbra has a community version.

I replaced my Exchange server with Linux mailing system zimbra, for me its reliable mail server,  as mail system  you can run qmail, postfix, eGroupWare, Scalix, Citadel, zarafa or Open-Xchange ..etc

http://www.zimbra.com/
http://www.scalix.com/
http://www.open-xchange.com/
http://www.egroupware.org/
http://zarafa.com/
http://www.linuxjournal.com/article/9619
http://www.citadel.org/doku.php
http://www.bowe.id.au/michael/isp/postfix-server.htm
http://www.bowe.id.au/michael/isp/webmail-server.htm
http://howtoforge.com/howtos/email/postfix
http://www.scalix.com/
http://www.iredmail.org/
http://www.linux-magazine.com/w3/issue/73/Citadel_Groupware_Server.pdf

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Will Zimbra work with Windows?
I need a full packaged Email Server, to work with operating systems like Windows 7 64bit, Server 2008 R2, SBS 2011 etc..   if it includes anti spam that would be fine but not necessary.

Currently there is no way to install Zimbra on Windows based system, they do not have a Windows Version of Zimbra server.

I need a full packaged Email Server, to work with operating systems like Windows 7 64bit, Server 2008 R2, SBS 2011 etc..   if it includes anti spam that would be fine but not necessary.

Thanks. Are there any others that can be recommended?