I have an email address for someone, where the hostname to the right of the @ sign is "mail.gongin.com.tw". When I try to do an MX record lookup on mxtoolbox.com, it reports "No Records Exist". Windows nslookup gives some information back but I don't see any "mail exchanger" data in the nslookup results. I've also tried an MX record lookup via this mail component and it too finds no MX records.
I sent two test emails to this person, each from a different email service. Both emails reached him and he replied to me.
How are these emails able to reach him? I imagine there must be some extra lookups that the sending mail servers are doing to find a mail server to deliver the email to, and if so, would like to know how that works.