mutt: how to change new mail checking frequency

[Mirko Parthey <mirko.parthey@informatik.tu-chemnitz.de>]

Hi,
mail_check doesn't have the effect I would expect:
When a message has been delivered to /var/mail/mpa, mutt takes about
10 minutes to notice the new mail, despite mail_check being set to small
values such as 5 or 1 (seconds).
Pressing ^L makes mutt notice new mail immediately, but I'd rather like
to automate the process. ;-)

Distribution: stable with all proposed and security updates applied

Package versions:
mutt 1.2.5-4
sendmail 8.9.3-23
fetchmail-ssl 5.5.3-1 (recompiled with Kerberos support)

Any ideas?

Regards,
Mirko