After an MX change, it can take up to 72 hours for all resolvers to see the new setting. In this article, you’ll learn why this takes so long, how to check the progress, and what role the TTL plays.
Why does it take so long?
To use our email security services, you must change the MX records in your DNS. However, it takes some time for these new values to be adopted everywhere.
DNS servers update their records only at specific intervals. Until then, they retain the previous values in their cache until they are replaced with the new ones. In addition, DNS is decentralized: Name resolution is distributed hierarchically across many independent servers whose structure resembles a spanning tree—from individual resolvers, through authoritative nameservers, up to the root servers. A change must propagate along this tree structure, and each node adopts it only once its cached record has expired. For this reason, it can take up to 72 hours in extreme cases for all systems to recognize your changed MX records.
I can already see my new values. Does that mean they have been adopted?
Not necessarily. If you perform a DNS lookup for your domain yourself and see the new values, this does not mean that they have already been fully propagated worldwide. Your local resolver may already be updated while other regions are still returning the old values.
You can use an online tool to check propagation across regions. This lets you see which regions have already switched to your new values:
Ideally, use several tools to get a complete picture of the current propagation status.
Does the TTL affect my propagation time?
A shorter TTL helps, but it is not a substitute for the actual propagation process.
The TTL (Time to Live) specifies how long a resolver keeps a record in its cache before querying it again. A shorter TTL therefore tends to result in the new values being adopted more quickly. However, this is not guaranteed: Some DNS servers and providers ignore the TTL. For those that respect it, however, it does have an effect.
A particularly short TTL is worthwhile especially if you frequently make changes to your DNS. For infrequent changes, this is generally not necessary.