[Dovecot] deliver problem ( Error: file_dotlock_create )

Hello all ( Postfix and Dovecot )

Trying to use deliver as mailbox_command with Postfix I get this error each time an email is arriving

deliver(xxxxxxxx): Error: file_dotlock_create(/var/mail/xxxxxxxx) failed: Permission denied (euid=3003(xxxxxxxx) egid=3010(smig) missing +w perm: /var/mail) (set mail_privileged_group=mail)

Doea this means I have to chmod 777 the /var/mail directory ?

Thanks a lot