Bt-Yahoo email?

[Ken]

A friend has changed dial-up from plain bt.com to the new bt-yahoo setup.

His old email address was --@talk.21.com, but his new one is --@btinternet.com,
which is the one he wants to use now exclusively.

The problem - email from Outlook Express sends/receives o.k, with the
btinternet.com address set as the reply address.
When he uses the browser email page, which is what he'd prefer to do, the
return address is always @talk21.com, even though it's sending from
@btinternet.com.
We've looked through all the various settings available on BT-Yahoo, but to no
avail. Is there something obvious we've missed?

Thanks in advance for any suggestions...!

Ken