mail()

hello all, I'm very new to php and the list, servers in general in fact... and I was wondering about the following: (maybe considered OT ?) if I put a form on a website that allows the visitor to enter a 'sendto' emailaddress and also a 'from' address, then I can use mail() in php to do the actual sending... but what happens if 2 bogus addresses are submitted? isn't there gonna be any infinite loop between my server and 'anywhere' because of 'not able to reach' type messages? and I'd rather not try it out :-) (as you can see I AM new to this :-), but there's nothing about it in the phpmanual mail() description (not that there should) and I have a deadline that's closer than I would like...) cheers, dominiq