Introduction
The files /etc/localdomains and /etc/remotedomains are used to configure if a domain is using remote or local MX records. They can be checked to determine the current configuration of a domain.
Procedure
To check how a single domain is configured:
# grep "domain.tld" /etc/{remote,local}domains
/etc/remotedomains:domain.tld
To list all local domains:
cat /etc/localdomains
To list all remote domains:
cat /etc/remotedomains