We have a client that the domain name has a cluster of DNS servers serving it but when it comes to mail routing... I've checked several different mx lookups including nslookup and things like who.is and mxtoolbox.com and to confirm the client showed me their DNS records and there are no MX records.

I was wondering .. how can they receiving emails if no MX specified?

The only thing I can think of is if there is a root A record pointing to (what is essentially a LAMP) server does it default back to that (at a stretch)?

  • check email routing option in cpanel or any other admin panel which you are using.. – technical trade Nov 19 '18 at 4:45

An A record pointing to the mail server handling the mail is enough, MX records are "optional", but preferred. So, if you have a suitable A record, this will be sufficient to deliver the mail.

  • So trying a TCP connect (e.g. by using telnet) to an A record's IP address at port 25 is sufficient to see whether an SMTP server is available? should I also check other records like e.g. CNAME or AAAA? – Uwe Keim Apr 5 '16 at 17:33
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    @UweKeim: It can be sufficient, yes. However, what I omitted is the fact that it's entirely possible to have a mail address user@example.org without having an actual A record for example.com. In that case, you would need the MX record pointing to a valid A/AAAA record. Also, if you want to use IPv6, you obviously need to check the AAAA record, not the A one. Why would you want to check some CNAMEs and which anyway? – Sven Apr 5 '16 at 17:48
  • Thanks, Sven. And sorry, actually I am not that expert in the DNS area. So no CNAME checking. alright :-). – Uwe Keim Apr 5 '16 at 17:59

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