Mail Sender

Hello All,
My unix (AIX 5.2) login is robk, my MS Exchange user name is rkapfer.

What I want to do is send mail as rkapfer while logged in (to unix) as robk.

I'm currently doing uuencode <pdf> <pdf>|mail -s"Subject" <recipient> works fine except the recipient sees me as robk@xyz.com. Replies to robk@xyz.com get bounced back, I'd like it to be sent by rkapfer@xyz.com. Good luck eh!

Thanks in advance