Service amavis even though part of group vmail who has mark 770
on '/var/spool/spamassassin', can't write lockfile to do a bayes
check.
Set '/var/spool/spamassassin' mask to be `777` with owner
`debian-spamd:vmail` recursive. so that amavis bayes check works.
MR !9
Default config is for domain example.org, which
is the testing domain.
User will be required to customise '90-dkim' with thier
own domain configuration, including generating dkim signing certificates.
MR !2
