Changing DNS MX records with a large TTL (Time to Live) to a new email server could cause some relays to route to the old email server

Issue

After Customer has switched their Corporate email server from, say, Gmail to Exchange by updating their DNS MX Record, the Companies' emails coming from ServiceNow instance, are still going to the Gmail accounts instead of Exchange.

This issue may only happen with emails coming from ServiceNow instance. Other emails coming from other sources may be correctly going to Outlook mailboxes via Exchange as expected.

Cause

TTL (time to live) of the DNS record which defines the MX Record is too high so the change is not propagated in a timely manner.

Resolution

The issue can be prevented by taking action before updating their DNS MX Record:

The TTL for the DNS record should be set to a very low value, for example 5 minutes.
Confirm that email routing is occurring as expected to the new email server.
Finally revert the TTL back to initial value.

If the MX record has already been updated where the DNS TTL was not set to a low value, ServiceNow cannot assist – However, after 2 days the propagation will be completed without any intervention from ServiceNow