testmxlookup domain
The testmxlookup command displays the names and IP addresses
of network servers that accept mail for a given fully-qualified domain name.
testmxlookup is used a troubleshooting and debugging aide.
The testmxlookup command sends a DNS MX query for the given
domain. Depending on the reply testmxlookup may also send a
follow-up A or AAAA DNS query. testmxlookup displays the hostname
and the IP address of every mail relay, and its associated priority.
The error message "Hard error" indicates that the indicated domain does not have any mail relays. The error message "Soft error" indicates a temporary problem while attempt to reaching the local DNS server.