Help with Mozilla Mail

[Tim Wood <tlwood@iinet.net.au>]

Hi,
I'm feeling very foolish as I cannot work out what is going on with 
Mozilla Mail.

I'm moving ISP and have accounts with iiNet and Bigpond. The SMTP is now 
set for mail.bigpond.com.

I can receive mail on both accounts, I can send mail form my iiNet 
account, compose in that account, and send with the above SMTP. When I 
try to send in the Bigpond account the mailer cannot contact the SMTP 
server, despite it's being the Bigpond server.
I'm in the process of moving my Debian subscriptions and have had to 
move the replies to my iiNet account to be able to respond to them.

I'm bemused by this and would welcome any suggestions.

TIA,
    Tim Wood