how do i tell what encoding is used in this : kwezaivhrgj1@xfwze.yff

first off yes it was an online challenge. this is not the original form it was first base64 encrypted and then encoded. it after we got this far. there was a hint dropped the contest is now over but some of us are still trying to figure it out, we know its an email address. we know its @gmail.com which means we know some of the letter changes but we still cant find out the type of encoding used, it seems to be custom. the .yff converts to .com so either f = o an/or m or ff=om not sure butthis kinda what i have so far f=o or m y= c x = g w= a z=I e=L which means xALIxxxxxxxxx@gmail.com is the translated portion i figured out b hand, some were shifted by 4 and some were shifted by 9 any thought or directions would be appreciated