Hi, @mike, and welcome to our Netlify community site.
I believe the issue occurring and the solution for it are both explained in more detail here:
The section titled “I did not copy my records before switching name servers and my email (or other service) stopped working. How do I fix this?” should help.
I suspect what happened is that domain was moved to Netlify DNS but not all existing DNS records were copied to our service first. This is the most likely root cause and there are solutions (more than one) discussed in the topic linked to above.
Regarding the specifics here, I see the following MX record for bangorwineandcheese.com:
$ dig bangorwineandcheese.com MX +noall +answer
; <<>> DiG 9.10.6 <<>> bangorwineandcheese.com MX +noall +answer
;; global options: +cmd
bangorwineandcheese.com. 21599 IN MX 0 mail.bangorwineandcheese.com.
Note, I’m including the dig commands to find the record. (I find dig to be indispensable for troubleshooting DNS issues.) If you don’t have dig installed locally you can use this online version of it here instead:
https://toolbox.googleapps.com/apps/dig/
So, there is an MX record but the target of the MX record itself doesn’t exist - the target being mail.bangorwineandcheese.com. Here is the dig output for that name:
$ dig mail.bangorwineandcheese.com
; <<>> DiG 9.10.6 <<>> mail.bangorwineandcheese.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NXDOMAIN, id: 13931
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 1
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 512
;; QUESTION SECTION:
;mail.bangorwineandcheese.com. IN A
;; AUTHORITY SECTION:
bangorwineandcheese.com. 1769 IN SOA dns1.p08.nsone.net. hostmaster.nsone.net. 1579021705 43200 7200 1209600 3600
;; Query time: 26 msec
;; SERVER: 8.8.8.8#53(8.8.8.8)
;; WHEN: Wed Jan 15 21:45:34 PST 2020
;; MSG SIZE rcvd: 122
Note, there was no CNAME, A, or AAAA record returned. Instead I got the SOA (start of authority) record for the domain. In other words, the DNS server said, “The name mail.bangorwineandcheese.com is unknown and so here is the SOA record instead.”
The solution for this will be to create the required records at Netlify and/or (you might do both if you like) revert to your previous DNS provider. Copying the required records to Netlify DNS is typically the “fastest” solution.
Please let us know if there are any questions about getting the required records copied (or about implementing a different solution).