I haven't found a way for dovecot to manage the mail directory ownership/permissions issue. Here is how I solved it manually: cd /var/mail mkdir a b c d e f g h i j k l m n o p q r s t u v w x y z chown root:mail ? chmod 775 ?
/var/mail: drwxrwxr-x 2 root mail 4096 Oct 31 11:02 a drwxrwxr-x 2 root mail 4096 Oct 31 11:02 b drwxrwxr-x 2 root mail 4096 Oct 31 11:02 c drwxrwxr-x 2 root mail 4096 Oct 31 11:02 d drwxrwxr-x 2 root mail 4096 Oct 31 11:02 e drwxrwxr-x 2 root mail 4096 Oct 31 11:02 f drwxrwxr-x 2 root mail 4096 Oct 31 11:02 g drwxrwxr-x 2 root mail 4096 Oct 31 11:02 h drwxrwxr-x 2 root mail 4096 Oct 31 11:02 i drwxrwxr-x 2 root mail 4096 Oct 31 11:02 j drwxrwxr-x 2 root mail 4096 Oct 31 11:02 k drwxrwxr-x 2 root mail 4096 Oct 31 11:02 l drwxrwxr-x 2 root mail 4096 Oct 31 11:02 m drwxrwxr-x 2 root mail 4096 Oct 31 11:02 n drwxrwxr-x 2 root mail 4096 Oct 31 11:02 o drwxrwxr-x 2 root mail 4096 Oct 31 11:02 p drwxrwxr-x 2 root mail 4096 Oct 31 11:02 q drwxrwxr-x 4 root mail 4096 Oct 31 11:05 r drwxrwxr-x 2 root mail 4096 Oct 31 11:02 s drwxrwxr-x 2 root mail 4096 Oct 31 11:02 t drwxrwxr-x 3 root mail 4096 Oct 31 09:28 u drwxrwxr-x 2 root mail 4096 Oct 31 11:02 v drwxrwxr-x 2 root mail 4096 Oct 31 11:02 w drwxrwxr-x 2 root mail 4096 Oct 31 11:02 x drwxrwxr-x 2 root mail 4096 Oct 31 11:02 y drwxrwxr-x 2 root mail 4096 Oct 31 11:02 z
Now I can login as 'brichards' and it properly created the mail directories under the 'r' directory.
/var/mail/r/brichards: drwx------ 3 nfsnobody nfsnobody 4096 Oct 31 11:05 /var/mail/r/brichards/ drwx------ 5 nfsnobody nfsnobody 4096 Oct 31 11:05 /var/mail/r/brichards//Maildir drwx------ 2 nfsnobody nfsnobody 4096 Oct 31 11:05 /var/mail/r/brichards//Maildir/cur drwx------ 2 nfsnobody nfsnobody 4096 Oct 31 11:05 /var/mail/r/brichards//Maildir/new drwx------ 2 nfsnobody nfsnobody 4096 Oct 31 11:05 /var/mail/r/brichards//Maildir/tmp
GR