E-mail/domain question

Hello

I had no idea where else to post this, so I hope this is an appropriate place.  I own a business and want my outgoing mail to look like it's coming from that particular website, instead of aol.  I asked aol if this was possible and they said no, although I know it is.  I believe it's possible in IE, although I'm not sure where.  Is there any way to change outgoing mail to look like it's coming from a different domain?

thanks!