Where MX records are concerned, the delay is
due to “caching”, not “propagation time”, at least not as the term is
normally used when discussing DNS issues. The only "propagation time"
(it's actually the “Cache Time to Live”) is the 30 minute TTL (Time To
Live) that Alentus puts on all of our DNS records. Other name servers
can cache responses from our name servers for up to the TTL that we set:
30 minutes. After the TTL has expired, all name servers should be
getting the new and correct MX record.