Help???

Please help the computer illiterate...

I have an email address at work that ends with "@rtui.net" BUT, when I send anything to anyone, in the "From" blurb it says "@swcyber.net" and no one up here knows why or how to fix it. Not only is this bad 'cause people typing a response to "@swcyber.net" gets it bounced right back to them, but it's been really hard for me not to crack any "cyber" jokes (which would be bad.)

I've check Preferences but can't find anything filled out to "@cyber.net" anywhere. Anyone have any ideas? *bats eyelashes hopefully*