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).

Now the first thing we need to make sure of before we start warming up an IP address is that all DNS entries are in place before the first piece of mail goes out the door. This includes PTR, A and MX records, SPF, DKIM value. Test that your configuration is setup properly with a validation tool such our DKIM Validator.

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. As users open your mail, your reputation will increase. As your reputation increases, ISPs will begin to accept more mail from your IP address.

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. Start with a few thousand messages to each ISP and then analyze your logs. See if the ISPs are accepting, deferring, rate limiting or rejecting your messages. Then you can adjust your daily and hourly volumes accordingly. Most senders can double their volume every 1-2 days if messages are being highly accepted throughout their IP warmup.

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, you might lose all reputation on that IP address. If that happens,  you’ll need to start over with the IP warmup process. 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? Our IP Warm-Up Guide provides a practical framework for managing IP warming.

Do you have questions about IP warmup? Something we missed? Comment below.