Why does my e-mail address change

[thepittsmn]

Why does my e-mail address when sending from outlook from MSN to hotmail and when someone replies I never receive their replies and it gets bounced back to the person replying?

 

[ezop12]

did you get underlivery error massge

which look like this

Undelivered Mail Returned to Sender

This is the mail system at host xxxxxx

I'm sorry to have to inform you that your message could not
be delivered to one or more recipients. It's attached below.

For further assistance, please send mail to postmaster.

If you do so, please include this problem report. You can
delete your own text from the attached returned message.

                   The mail system

xxxxx: User unknown in virtual alias table