What's the best email server software for Windows Server?

What's the best email server software for Windows Server? What are your experiences?

iMail
MailEnable
SmarterMail
???

I personally think MailEnable is the best. It should be the most used one on the Internet as there's a free version distributed with control panel like Plesk.

iMail is overpriced.

I think imail is best, its service are good.

MailEnable is what I have used for almost 10 years.