[TYPO3] Disable E-Mail Verification / Check - To use mail at localhost

[Christian Ruppert]

Hello,

I have a typo3 on my local machine. (with mercury)
Now I'm trying to test some stuff, the "front end user registration" 
plugin, for example.

But I got the problem that an email adress like "mail at localhost" is 
rejected (not valid)
Is there any "global option" where typo3 checks the integrity of entered 
mail adresses. I looked around in the extension, but i think typo3 takes 
care of the check. I now something about php, so even if there is no 
"option" i may disable the check by hand, if anybody can tell me, which 
file (xyz.php) takes care of the check..

Thanks,

Christian