Well, if you came to the irc, you'll probably know the answer. I dont think admins/Gms will tell you the email you used for registration. I suggest you to check all the emails you use/used, to see if there're any emails sent by PWO, if there is, that's the email you're looking for.
However, if you cant find any, the only way you can play PWO again, is to start from the beginning- Register a new account
Btw, registration will be opened on next Friday to Saturday(You can refer to Vash's announcement)
Hope this helps and good luck!