I've got a domain on dns.he.net that only has an SOA record, NS records, and one MX (pointing to a totally different host). Does my domain need an A record? Currently nslookup fails since there is no IP associated with it. But mail seems to get to the MX host just fine.
Just to add... for the purposes of SMTP, you strictly don't need an A record at the apex unless you do not have an MX record. Most mail transport agents (MTAs) will, by default, look for an MX record first and if one is not found look for an A record and attempt to deliver to wherever that A record points. I'm not advocating you do this, so by all means use an MX record for mail, but just know that this fallback behavior exists.
nslookup is failing because by default it asks for an A record.
~/bin/vmware@precious% nslookup -query=mx umich.edu Server: 192.168.1.1 Address: 192.168.1.1#53 Non-authoritative answer: umich.edu mail exchanger = 0 mx2.umich.edu. umich.edu mail exchanger = 0 mx3.umich.edu. [ ... ]
dig instead, its default response is more verbose.