I’m just curious as to why I’d go through the whole glue record setup and not just point my mx records to my MIAB box? Having never used MIAB is that going to break something? It seems overly complicated.
I assume if I skip it then I just create my dkim/spf/dnnsec records by hand?
Inside MIAB, there is a nameserver called nsd. This is a very powerful utility which allows your box to host all the DNS records required to run your services. An MX record is just one of many mail-related DNS entries you need. Others include: SPF, DMARC, DKIM, DNSSEC, and others.
The glue records are what allow you to tell the Internet that you’ve got nameservers and they reside at a particular IP (specifically that they can be found at the IP of the MIAB). Then what I mention above is built on top of those glue records to allow all the services to function.
As long as you’ve got the records required setup somewhere, and these can be found publicly, then you should be fine. The status screen may not be all checkmarks/green (you’ll see some errors), but it will work. This is as if you were using External DNS.