To use our mail security services you have to change your MX-Records inside your DNS. Your newly updated values will take time to propagate.
How long does it take?
DNS-Servers do update in certain intervals which means that old settings are stored in their cache until they get replaced with new values. Since DNS is decentralized and its structur is similar to a spanning tree it takes time for your new values to reach the roots. This is why it can sometimes take up to 72 hours (in extreme cases) for your MX-Record changes to be recognized by everyone.
When I check my DNS I can see my new values already!
Even if you yourself can do a DNS-Lookup for your domain and see the new values it does not mean they are fully propagated yet. To check for this propagation you can use an online propagation tool like DNS checker or Whatsmydns. This way you can see what regions should be updated with your new values.
Here is a short list of some tools you can use to check the propagation:
Always use multiple tools to get a better picture of your current propagation.
Does TTL affect my propagation time?
Yes, TTL affects your propagation time. Though it does not prevent DNS-Servers/ISP's to ignore TTL, it will affect everyone that does respect it.
A shorter TTL will result in a faster propagation but is not necessary if you are less likely to make frequent changes to your DNS.