Warming Up an IP Address

When you add a new dedicated IP address to your account, you need to warm it up. You also need to warmup your IP if you haven't sent on it in more than 30 days. Warming up your IP allows you to gradually send more emails over your new IP to establish a good sender reputation.

IP warming is the practice of gradually increasing the volume of mail sent with a dedicated IP address according to a predetermined schedule. This gradual process helps to establish a reputation with ISPs (Internet Service Providers) as a legitimate email sender.

When an ISP observes email suddenly coming from a new or "cold" IP address, they will take notice and immediately begin evaluating the traffic coming from that IP. Since ISPs treat email volume as a key determining factor when detecting spam, it is best to begin sending a low to moderate volume, eventually working your way up to larger volumes. This gives the receiving email providers a chance to closely observe your sending habits and record how your recipients engage with your email.

A gradual warmup does not always guarantee a perfect sending reputation. It is still important to follow sending best practices.

It is much easier to establish a positive reputation as a new sender, than it is to repair an existing reputation.

Warmup types

There are 2 ways to warmup your IP. If your dedicated IP is relatively new, or you've never had one before, you need to warmup your IP manually. If you are adding new dedicated IPs to existing warm IPs, you can automatically warmup your IP with the UI or the API. When your IP is being warmed up, your hourly sending limits are in the table below in the "Automated IP warmup hourly send schedule" section.

Manually warmup your IP

To manually warmup your IP, you need to gradually send more and more email over your IP address at the rate in our suggested IP Warmup Schedule. When sending through a new domain and IP address, you are inherently more susceptible for receiving blocks, deferrals, and other reputation-related email errors because recipient servers do not recognize your mail. It's important to build this reputation over time, which is why we recommend the throttling via IP warm-up as soon as you receive your new dedicated IP. This is a manual process for users with 1 IP and would involve that you segment your sending by breaking up contacts into smaller lists and scheduling your campaigns, as a suggestion. The goal with IP warm-up is to avoid and/or mitigate deliverability issues that come with lack of reputation such as blocks, deferrals, or bounces.

The goal of warming up is to ramp up your sending volume to your anticipated “normal” levels. For example, if you have a Pro 100k account, you don't need to warmup to 2 million emails as that will exceed your account limits and is unnecessary if you're only sending 100,000 emails a month.

Automated IP warmup

In order to take advantage of automated IP warmup, you need to have two or more IP addresses so you can warm up one automatically while the other (already warm IP) acts as an overflow for any emails that exceed the hourly limit. Automatic IP warmup allows Twilio SendGrid to throttle the number of emails for you, avoiding you damaging your sender reputation.

To set up automated IP warmup in the UI:

  1. Go to Settings > IP Addresses.
  2. Click the action menu for the IP you want to warmup. This brings up the Edit Your Dedicated IP Address screen.
  3. Select Use Automated IP warmup.
  4. Save the Edit Your Dedicated IP Address screen.

Automated IP warmup API

You can also put your IP address into warmup mode with our Automated Warmup API - this automatically throttles traffic sent through your new IP according to our warmup schedule. Any email requests that exceed this hourly limit will overflow to any other existing warm IPs on your account.

When automatically warming up an IP, SendGrid limits the amount of email sent through that IP per hour. Any email requests that exceed this hourly limit will overflow to any other existing warm IPs on your account. You must have 2 dedicated IPs to access the automated IP warmup. If you do not have any other warm IPs, we will use an IP from one of several SendGrid shared IP groups, which will be determined based on your sending reputation.

Automated IP warmup hourly send schedule

Warmup Age (Days) Hourly Email Limit
0 20
1 28
2 39
3 55
4 77
5 108
6 151
7 211
8 295
9 413
10 579
11 810
12 1,000
13 1,587
14 2,222
15 3,111
16 4,356
17 6,098
18 8,583
19 11,953
20 16,734
21 23,427
22 32,798
23 45,917
24 64,284
25 89,998
26 125,997
27 176,395
28 246,953
29 345,735
30 484,029
31 677,640
32 948,696
33 1,328,175
34 1,859,444
35 2,603,222

If you are sending transactional emails, you do not need to focus on a strict IP warmup schedule, as you cannot control the rate at which transactional emails will be triggered through the account. If you are sending marketing emails, you will need to follow some sort of IP warmup; this involves gradually increasing your sending day by day on this new IP. The slower you can warm up the better. This way, you can locate and fix any anomalies and issues that arise when you first begin sending, helping your deliverability long term.

Why don't other ESPs require IP warmup?

Some email service providers do not offer dedicated IP addresses to their customers - they place all of their customers on shared IP groups by default. Warming up is not required for a shared IP group - SendGrid handles this automatically.

Having a dedicated IP allows you to control your own reputation completely, and prevents your sending from being impacted by the reputations of other SendGrid users.

Additional Resources

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