I'm new to mail servers and still trying to understand all the components.
What I read is that there are many MTAs, but the 4 common ones are qmail, Postfix, Sendmail, and Exim.
I also found this list of mail servers. http://en.wikipedia.org/wiki/List_of_mail_servers
What's confusing me is that mail servers like Zimbra and Atmail are listed at the same level as qmail/Postfix, etc. Are mail servers and MTAs the same thing? I thought (correct me if wrong) that a mail server includes an MTA as one of its components.