Sort User List

ok... Our server just got hacked, and I have to add all these users in by hand, into the controll pannel of our Raq3... to make this job easier I want to write a script on my machine to sort all the users and there email addresses into easy to use files. Only problem: I have no clue how to use the fopen and explode commands!!! =++ The Situation ++= I have a list of users that is setup something like this, line after line: emailaddy@domain username dada@www.dadauniverse.com dadauser meme@www.memecenter.com meami how could I do a explode and use a array to sort ALL of them (there are a TON) into different files according to there domain?? The file with all the users is enormous, and is in no order at all... I know I would have to do a fopen() then a explode("\n") or something like that, but I am not sure, anyone have a clue??