The interviewer asked me one question that, Do you have any idea about the jse mail server configuration?

Can i know how many mail servers are available for Redhat linux?

could anybody help on this?

Many

sendmail
procmail
squirrel
evolution
etc...

When interviewing don't be afraid to admit there's something you're not an expert at. Employers often seek people that know everything but actually have a core they are interested in. If you try to pretend you've heard of something you haven't you'll quickly be tripped up. An employer is more likely to hire someone who hasn't worked on a given application than someone that lied about something during the interview.

I've never heard of jse by the way. Also note that many companies actually use products but call them by the names they use for them. (e.g. Here we call our Nagios "EMA". If we interviewed people and asked "do you know EMA monitoring" we'd get a blank stare.)

On Linux there's usually at least 5 ways to do anything so trying to know it "all" just isn't practical.