[Evolution] Suddenly can't send mail

[Andy Coleman <incoming andycoleman me uk>]

Hi

Fedora 8

When I try and send any mail I suddenly get the following :-

RCPT TO <address> failed...  mailbox unavailable

There is nothing wrong with my ISP. I/C is OK and I can send and receive via my Windows PC.

I've removed the Evolution package and reinstalled it to no avail.

Is there anything I can look at to identify the exact cause ?

TIA
Andy