What is DNS propagation?
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You've just updated your SPF record, saved the change, and now you're wondering: when will it actually kick in? That waiting period is called DNS propagation.
When you update a DNS record, the change lands instantly on your authoritative DNS server (the one that holds your official records). The problem is that the rest of the internet doesn't talk directly to that server every time. Recursive DNS servers around the world cache your old record to save time. Propagation is the process of all those caches expiring and fetching the new data.
How fast that happens depends on your TTL (Time To Live) setting. TTL is a number you set on each DNS record that tells caching servers how long (in seconds) to hold onto it before checking for updates. A TTL of 3600 means servers cache your record for one hour. A TTL of 86400 means they hold it for a full day.
The practical window is 24 to 72 hours for full worldwide propagation, though in practice most major mail servers pick up changes within a few hours. The long tail is rural ISPs and legacy resolvers that don't refresh as often.
During propagation, different senders may see different versions of your record. One mail server queries a cached copy and gets your old SPF rule. Another queries a freshly-refreshed resolver and sees the new one. That's why testing immediately after a change can give you misleading results.
A few things that help you get there faster. First, lower your TTL before you make the change. If you drop it to 300 seconds (five minutes) a day or two in advance, old caches clear quickly and your update spreads in near real-time. After propagation is complete, you can raise TTL back to something sensible like 3600. Second, once you've made the change, verify it with a DNS lookup tool rather than just trusting that it worked. Our free SPF checker will query live DNS and show you exactly what the world is seeing right now.
And if you're in a real bind, our SOS hotline is free. We'll help you figure out whether the issue is still-propagating DNS or something else entirely.
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