testmxlookup(1) on Linux
The text 0b206e9c9469, as Debian 12 (Bookworm), Debian 11 (Bullseye) shipped it.
Look up mail servers for a domain
Flags it lists
-
--dnssec -
--sts -
--sts-cache-disable -
--sts-cache-enable -
--sts-expire -
--sts-override -
--sts-purge -
--udpsize