[Dovecot] question about /var/spool/mail/xxx

this is Redhat 6.3 I installed sendmail and dovecot. but sendmail can continue send mail as MTA all mails go to /var/spool/mail

this is problem for dovecot. dovecot cannot get it goto dovecot inbox.

if setup mailbox poing to /var/spool/mail/%u, it is workable but if set up maildir to somewhere else ,I cannot receive mail by dovecot.