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Pros
Pro Easy to use
Most Linux distributions that come with Exim, come with sane Exim default configurations. Changing default values and slightly adjusting configuration is relatively easy. On the other hand, building a completely new Exim configuration file from scratch might not.
Pro Good documentation
Exim provides thorough documentation with great examples.
Pro Sendmail compatible
Exim is a drop-in replacement for Sendmail.
Cons
Con Missing some features
Missing featues like: webmail, ActiveSync, WebAdmin.
Con No support for some protocols
No support for: POP3, IMAP, POP3s (POP3 over SSL).