Getting right EMail...

Hello ! I got a shop-system where the user has of course to enter his address and his email. The problem: Many users type-in WRONG Emails (about 30%). Things like "...@aol.de" instead of "...@aol.com", same with yahoo.de/com, mostly only a letter is missing ("Katharin@somehost.tld" instead of "Katharina@somehost.tld"). I use syntax-checking with a reg-expression, which works fine but can of course not find the errors shown above. I tried use the script found at http://px.sklar.com/ -> network, which connects directly to the EMail-Server and tries to identify the user. Unfortunatly, this doesn't work correctly, because some email-servers always say "well, thats a correct address". Yahoo for example tells sometimes right, sometimes on a unvalid name -> ok and sometimes on a valid name -> not ok... So this is not a save way to check an email. Any other ideas ? Martin