Email validation

Hello to you all!

I'm facing a problem with a scrip that can validate a form witch accept only
as input email address.

I have seen many scripts on the net and  were very interesting but I'm not
able to implement those scripts on my need.

 I'm explaining myself better!

I have a form to collect a User Input Email address, 

After a script to check the syntax of the user email is correct.

Then check the mx record if really exist.

At the end if the user input (email) meets all my requirements the pass it
(store) in a DB.

Please I'll be grateful   to all your possible solutions

Thanks.