Problem sending email

My husband has an iBook with OS9,Outlook Express 5.0. I
have a PC with WinME and OE6.0. They are networked. We
have recently moved from Sympatico to Rogers cabe. We are
happy with the result but here is a problem. We have our
own business domain. Most of our mail goes through the
server that hosts that domain.
For personal mail, we want to use the emails from Rogers.
My Rogers email works fine as does my husbands that I set
up on the PC. However, the same email address that I
tried to create on his iBook won't work. All the settings
are correct as I went over them with Rogers. When I send
a test email, I get an error message that says:
Authentication required. Error 5530.
In 'SMTP server requires authentication', I clicked "log
on using" then his email and his password, just like
Rogers told me to do. It works on the PC but not on the
Mac. What can I do?