mutt won't send emails, kmail does

[geoffthur@ntlworld.com]

Hello list,

I've switched to using mutt, but I can't get it to send emails. It's a 
new install of sarge, and is bang up to date. Kmail does send emails - 
including this one. I don't seem to be able to send local mail either - 
or if I can I can't see where they are going. I've tried mailing root, 
and have root: geoff in /etc/aliases, but the mails seem to disappear. 
Root can mail user geoff, though. This suggests to me that it's going 
to be a blatantly obvious group or permissions problem, but I can't see 
where. User geoff is in the mail group, and has been in and out of 
Debian-exim group, but neither worked. I'm using exim4 at the moment, 
but have tried postfix also. netstat -lpetu shows exim4 to be 
listening.

My .muttrc looks like this:

set folder=~/Mail
set sendmail="/usr/sbin/exim4"
unset bounce_delivered
set copy=yes
set delete=yes
set nomark_old
set move=yes
set postponed=+postponed
set record=+outbox
mailboxes  +geoffthur +green +suspect +science +crt-users
subscribe debian-user

At one stage I was getting an error message when I tried to send emails, 
but I forgot to write down the error, and can't remember how I got rid 
of it. Currently the mail claims to have been sent, but doesn't go 
anywhere apart from the outbox folder, where the copies are going. When 
I start kmail it finds them all and wants to send them. I have been 
changing things backward and forward for days now, and have googled and 
RTFMed in vain. Surely kmail would use exim4? In which case the problem 
is in how I have set mutt up? I'm confused, and know the answer must be 
blindingly obvious.

Sorry if I've failed to give enough info for you to help.

Geoff