SOLVED: warning: do not list [FQDN] in BOTH virtual_alias_domains and relay_domains

Some time ago I asked what the subject error message means.
Nobody replied, and web searches only turned up a lot of
other people asking the same question and not getting
an answer.

The warning is telling you that one of your virtual
alias domains is a subdomain of a domain you are
using in a non-virtual context.

/etc/postfix/main.cf:
mydomain = example.net
virtual_alias_domains = obscure.example.net

It happens if the variable parent_domain_matches_subdomains
contains "relay_domains". It's a feature.
It's warning you that older Postfix versions' tendency to match
subdomains is being phased out and you may need to
revisit your maps or config file, in case you were
depending on it.

I hadn't defined parent_domain_matches_subdomains.
You can find its current value with

postconf -d | grep parent_domain_matches_subdomains

Perhaps the feature would be a little more obvious if
the parent_domain_matches_subdomains definition in
postconf(5) were changed. s/What/List of/



HTH.

Cameron