I need to know someone who can guide me on good email servers. can anyone give me some idea?
It depends on which platform you intend to install it on, if you need to both receive and send emails etc. Anyway, Vaadin forum is not the correct place for this question, try, for example,
superuser.com
Googling might be the best way to find your answer. or may be something like this be good for you. http://mailserver4u.info/