As far as I can see (looking at EFnet/DALnet anyway), the raw does contain the [email]user@host[/email] of the person that set the ban. Were you looking at /debug info?
Examples:
DALnet: <- :slimey.uk.eu.dal.net 367 Mentality #mirc *!*TurkRock@* GuardianX!mircbot@help.mirc.org 1122983030
EFnet: <- :irc.kagmir.ca 367 Mentality #mirc *!*@cache5-2.jed.isu.net.sa BluFire!blufire@hydra.lod.us 1121122774
Regards,
