IP Warmup: How to Gain Credibility with ISPs
Switching Email Service Providers (ESPs), changing data centers or simply adding a new IP address to your outbound mail traffic will most likely require you to “Warm Up” an IP address. Warming up an IP address means establishing a reputation with the Internet Service Providers (ISPs) so you can send more mail and at a faster rate. I like to compare IP reputation to an ISP like a new neighbor moving in next door. You most likely won’t hand them a spare key to your house (Whitelisting at an ISP) right away. They’ll need to gain your respect by meeting you several times and getting to know you (sending a little bit of mail to users who are opening messages).
Before the first piece of mail goes out, verify the sending IP’s forward and reverse DNS and the domain’s authentication. For Bird, use the records provided by the sending-domain setup, including DKIM, the return-path and DMARC. An MX record on the visible From domain is not a substitute for these checks.
Slow and steady wins while thinking of volume to the ISPs. The last thing you want to do is flood an ISP with all of your traffic right away. Choose the email addresses or channel that has the most engaged subscribers and mail to those first. Watch acceptance, deferrals, complaints and recipient engagement together. Opens alone do not establish reputation, and neither an open nor a completed warmup guarantees inbox placement.
You will hear many different opinions on how many messages each ISP will accept per hour or per day as you are starting to send messages on your new IP address. The most important thing is to listen to the ISP on what they are telling you through failure analysis. Set an initial volume appropriate to your provider’s plan and your opted-in audience, then analyze your logs by mailbox provider. Check whether messages are accepted, deferred, rate limited or rejected before increasing volume. There is no universal “double every day” schedule. Google’s sending-volume guidance calls for gradual increases and adjustment to recipient feedback; hold or reduce volume when delivery problems appear.
When your IP address is finally “warm” continue to follow best practices to keep your IP reputation intact. Keep in mind that if your IP sits for too long, its past sending history may no longer be a useful guide to the volume receivers will accept. Resume gradually and inspect the new responses. ISPs don’t like to see spikes of valleys in volume, so keep a consistent volume and cadence of traffic on your IP address to maintain the best reputation. Any time you add a new traffic stream, domain record or make other changes in your sending configuration, it is best to warm that traffic up with a slow approach.
-Brady Edwards
P.S. Want to learn more? The current Bird IP warmup guide explains the managed ramp and monitoring for Bird dedicated IPs. Those controls are separate from the general advice in this 2017 article.
Do you have questions about IP warmup? Something we missed? Comment below.