postfix cannot connect to milter-greylist sock

From: vagabond <vagabond_at_blackfoot.net>
Date: Tue, 23 May 2023 16:31:58 UTC 
postfix doesn't want to connect to milter-greylist.sock:

maillog:
postfix/smtpd[13700]: warning: connect to Milter service 
local:/var/milter-greylist/milter-greylist.sock: Permission denied

# ls -l /var/milter-greylist/milter-greylist.sock
srwxr-xr-x  1 mailnull  mailnull  0 May 22 16:43 
/var/milter-greylist/milter-greylist.sock

# grep postfix /etc/group
mail:*:6:postfix
mailnull:*:26:postfix
postfix:*:125:

I've stopped and restarted the postfix service, thinking it didn't 
belong to the mailnull
group for some reason.

Added postfix to the mailnull group using vigr.

what am I missing?
Thanks,

Gary