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 warm up 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 Internet Service Providers (ISPs) 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.

Warming your IP address

A new IP address can be placed into warm up using the automated IP warmup feature.

If you have one or more existing warm IP addresses, the newly added IP address will slowly send more and more traffic over time. Any additional volume above that exceeds the hourly send schedule will be routed through your existing warm IP address(es).

If you do not have an existing warm IP address, any additional volume above the hourly limits will be routed through SendGrid's shared IP address infrastructure.

If you prefer to manually control the warm up schedule by gradually sending more and more email over your IP address, you can reference our recommended IP Warmup Schedule for guidance on how much mail to send during the warm up process.

If you only have one dedicated IP address, you cannot use the Automated Warmup API. You need at least two dedicated IP addresses to use this feature.

Automated IP warmup

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.

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. 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. SendGrid Free and Essentials customers leverage our shared pools and therefore do not require a warm up strategy.

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. SendGrid customers utilizing dedicated IP addresses are strongly encouraged to undertake a warming program in order to avoid possible deliverability challenges that may be faced when sending from new IP addresses.

Additional Resources

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