dovecot (+sendmail) fails to get email into thunderbird

[jo land]

> # %u is replaced with the username that logs in
> mail_location = mbox:~/mail:INBOX=/var/mail/%u
>

if i change the mail location into: mbox:~/mail:INBOX=/var/mail/%u

mail.log says:

Dec 14 14:24:26 pie dovecot: imap(update.site1): Error: user update.site1:
Initialization failed: Namespace '': mbox: mbox root directory can't be a
file: /var/spool/mail/mail