Little trick that may be of help in determining if the server you are trying to extract your email from is 'alive':
go to the command prompt (start, run, type in 'cmd')
At the dos prompt type 'ping mail.btinternet.com' - this should give you the response times from the server - if it's down it will tell you that. It won't tell you if their security module is working or not or whether the server itself is fully operational in other respects but it's a starting point anyhow.
Find it strange that they don't support Outlook - the settings are pretty basic and are similar to Outlook Express which their system is able to configure automatically via their award-winning-not Internet Installer program.
Glad I'm not with them anymore - long live Telewest Broadband