Email Server Recommendations

[UCWebDesigns Webmaster]

I am still pretty new to linux although I have been around it for a few
years now.  I am currently the Network Admin / Web Admin / Lead
Developer at a Tempe based company that I am currently re-developing
there ASP,MSSQL,EXCHANGE site/network to a php/mysql website and
servers.  Development is almost complete and my new server is up and
running but I need some recommendation on email server software.  I am
looking to something that can be configured relatively easily.   Any
recommendation, ideas, and/or feedback are welcome.

Thanks
Rob