If you mean check the syntax of the supposed email so it looks like an email, then yes.
Do google for "email syntax validation .net"

IF you mean check to see THE email entered actually exists in the world, yes and no. You can check the last part of the email (the domain name) by doing a dns lookup. But not many domains I know of return a list of valid email addresses at their domain, otherwise spam would be 100% worse.

So while you could check for [email protected], by verifying msn.com is a valid domain, you couldn't verify there is actually a Steve there.