why would replicated to server ask for extra fs permissions?

I think I'm near getting a simple replication, but on server which is still "empty" I get:

Initialization failed: Namespace '': mkdir(/var/spool/mail/ccnr.biotechnology/nr412/Maildir) failed: Permission denied (euid=1187(nr412) egid=513(Domain Users) missing +w perm: /var/spool/mail, we're not in group 12(mail), dir owned by 0:12 mode=0775

but repl from server runs just fine and their configs are virtually identical. What I missed?

many thanks