I'm not sure if I follow you, but it sounds like you want a copy of all of the mail to reside in both /var/spool/mail/<user> and in ~user/mbox. However, since that seems pretty odd, I'll guess (and probably guess badly) that you really didn't want to use /var/spool/mail at all
To have all delivery go to ~user/mbox, you can set the default_mail_env variable in /etc/dovecot.conf as follows: default_mail_env = mbox:~/:INBOX=%h/mbox:INDEX=%h/.imap_index
(the INDEX part is optional, but helpful.)
-Rich
The dovecot docs say that support for the automatic appending of /var/spool/mail to a ~user/mbox (as is done by UW-IMAP) may be implemented in the near future. Is this still the case? And if so, is it far off?
why not directly deliver to ~user/mbox ?
darix