Problem with Dovecot

[Keir Snow <snow.keir@gmail.com>]

Bit of a newbie here so please bear with me!

I've installed Dovecot on my debian squeeze virtual server.  I managed
to configure it using system users and it seemed to work.  However
over the past week or so it has simply not been working.  mail I send
to myself (ie keir@mydomain.org) does not appear in the webmailer
(roundcube) or mutt as it did previously yet it does not bounce
either.  There are no relevant messages in /var/logs/mail*. It is
quite possible that I've flipped a switch somewhere that I have
forgotten about, just wondering what the first things I should check
in trying to solve this problem are?

Thanks

Keir