[Mashiro]

A very strange situation going on here. I have never experienced this with any of the services that I used for custom domain e-mail addresses (Zoho/Yandex/former GMAIL Apps) and DNS service providers (HE.net/Cloudflare/1984/Cloudns). I have never used it with a hosting control panel and its DNS servers though nor with the DNS servers of the domain registrar.

Sounds to me like there is something not properly working with DNS or the DNS records are indeed still not setup right. I'd be willing to look into the issue if you are interested @deanhills. That of course requires access to a few parts of your server/services used for this. Basic diagnostics for DNS could be done with https://www.whatsmydns.net/. You type in the hostname of the corresponding DNS record (e.g. mail.domain.ext) and select the corresponding type (e.g. CNAME) and see what the replies are. So if you use the hostname yourdomain.ext with the type MX the reply should be the MX record you setup with the MX server. If it isn't then there is something already wrong. Same with the other records. Of course all of this can also be done via NSLOOKUP but NSLOOKUP can only check from your location while the linked site checks from multiple locations world wide.

The only issues I ever had so far are a) DNS update simply takes its time sometimes (doing too many changes during this time can cause even longer waiting time ) and b) some domains are banned by the services (like all the stuff from afraid.org DNS or at the end Zoho also even banned eu.org when they still had the free service).