IP Address Warmup Guide – Maintain Your IP Reputation

IP Address Warmup Guide – Maintain Your IP Reputation - Dedicated SMTP Servers for Bulk Email Marketing


Inside this ip address warmup guide you will learn the right way to establish and maintain a good reputation for your new IP.

IP Addresses 101

As you probably know already, IP addresses identify different computer servers around the world. You can identify an IP address by its four different numbers separated by three periods. It’s a pattern like this: aaa.bbb.ccc.ddd. For example, is an IP address. Each number in an IP address can go from zero to 255.

While there are a limited number of IP addresses available, there are still plenty to be had. Almost any email service provider or web host has several “blocks” of unused IP addresses waiting for new customers. Don’t let anybody tell you they’re in short supply, and you have to grab one while you still can.

IP addresses are important to email marketers because your IP address is directly tied to your sender reputation. And sender reputation has perhaps more impact on your deliverability rates than any other factor.

Sender Reputation makes or breaks your inbox placement rate. But it all starts with the reputation of the IP address you’re sending from.

This link between IP addresses, sender reputation and improved inbox placement rates is the #1 reason why people leave a shared IP address for a dedicated one, or decide to move to a new IP address at all. On a shared IP address, you can only be as good as the least trusted sender.

Email delivery is based on reputation, but unfortunately, new IP addresses don’t come bundled with a reputation score. When you unwrap your new IP address, your first step is to establish a positive reputation to let the ISPs know you are a legitimate sender. So how do you successfully get delivered with an IP with zero reputation? The answer is—warm it up!

What is IP address Warmup?

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 warm-up does not always guarantee a perfect sending reputation. It is still important to follow best email marketing practices.

Why do we warm up IPs?

  • Unfortunately, the need to warm up IP addresses is mostly the result of a tremendous number of bad actors who abuse the medium of email to send recipients content and messages they didn’t agree to receive. The result of this is that inbox providers inherently (and necessarily) distrust unfamiliar senders. Because of this, IP warm up is necessary for anyone who wants their messages getting to the inbox.

Benefits of IP Address Warmup From the ISP Perspective

Warming up an IP address means that you start sending low volumes of email on your dedicated IP and then systematically increase your email volume over a period of time. This gives ISPs the opportunity to recognize, identify, and evaluate your sending practices. During this period ISPs evaluate your sending behavior and content to see how healthy your list is and how committed you are to deploying relevant information to responsive users. They even look at things like how many users opened your email, scrolled to the bottom, or moved your message to other folders.

The goal of warming up is to ramp up your sending volume to your anticipated “normal” levels, allowing the ISPs to gain trust in your sending behavior. You want the ISPs to learn your usual sending volumes so they can identify any suspicious behavior (i.e. spammers are known to infiltrate inboxes with malicious email by frequently switching IPs to circumvent ISP security checkpoints).

For example, both Hotmail and Yahoo! limit the daily sending allowance for all senders. They assess your reputation to determine your normal volume and then once that volume is exceeded, they block the “excess” email. However, as they get to know you, they will increase your daily limits. It’s all about establishing patterns and a circle of trust.

Benefits of IP Address Warmup From the Sender Perspective

This warm up period provides you with an opportunity to remedy any issues you may have prior to deploying to your entire database. With the right email deliverability tools, you can determine if ISPs are throttling your mail and see if your email is ending up in the inbox. Check your delivery rates by campaign, ISP, day, time, etc. and adjust accordingly.

Additionally, it’s a perfect time to reassess your content—identify which emails are generating the most (or least) engagement and find out why. By dealing with a small sample, you can more easily identify patterns and then, when your IP is warm, deploy the winning messages to your entire database.

As a sender, warming up your IP provides a very unique opportunity to monitor and optimize your entire email campaign. You’ll also find that the good reputation you build during the warm up period will make your life much easier. Instead of chasing down problems, you can focus more closely on honing your acquisition strategy and working on product enhancements. Every delivered email increases your overall opportunity and teaches you more about your customers and their needs.

Email Volume and Timeline

For IP warm up, the volume of email and over what period of time is different for all senders. How many emails you send depends on your own total email volume, but in any case you must send enough email at enough frequency so that your email reputation can be tracked.

As a general baseline, you should send at least 50,000 emails per month at least twice per month (for 100,000 emails total) in order to need to warm up your IP. (This means that if your email volume is going to be really small but steady on a dedicated IP, you don’t need to worry about warming up—you’re off the hook!) Most reputation systems only store data for 30 days, so you should not go 30 days or more without sending on an IP. If you do, then you will need to warm it up again.

Where To Start?

The biggest hurdle is knowing where to start.

1) First, choose a segment of your email file to warm up. For instance, choose your welcome message as your trial segment for your new IP. Welcome messages do several good things; they serve as a permission reminder, they reiterate your value proposition, and they have calls to action to generate response. The point is to select a mail stream that has strong permission practices. This will help build your reputation and solidify your legitimacy as a sender in the eyes of the ISPs.

2) Once you’ve decided on a segment, determine the amount of email you should send. Once you determine your volume, send that same number of emails for several days in a row and then gradually increase your volume. This process can last up to 60 days. However, the majority of MailBrainiers clients warm up their IPs within 30 days with some completing the process in as little as 1-2 weeks. To determine speed, use your results as a guide. If you are attaining good email deliverability with high engagement rates, then you can try to speed up the process. However, if you get throttled, tap the brakes and slow it down.

Below are a few suggested schedules for ramping up your sending.

Sample IP Address Warmup Schedules

(Please note: These sample schedules are intended to be a suggestion only. Every sender is different and you will need email deliverability experts to help you determine the right warm up volume and frequency for your email marketing program.)

Promotional Emails

Conservative Approach:

Estimate your total monthly email volume and divide that number by 30. Then, try to spread your sending evenly over the first 30 days, based on that calculation. For example: if you will send 90,000 emails/month, you should start off sending 3,000 per day over the first month.

Aggressive Approach:

Instead of dividing total monthly volume by 30, divide it by 15. For example: say you still need to send the same 90,000 email/month, but you need the emails to reach your recipients in half as long of a time frame, send 6,000 per day for the first 15 days.

Transactional Email

Established businesses:

If you are already sending a ton of email, and you decide to move to an ESP for the first time or switch to a new vendor, you should migrate your sending a little bit at a time. One way to do this is to split your traffic and move small portions of it to the new IP over time. Alternatively, if you are already maintaining multiple mail servers, you can move your servers over to your new IP one at a time.

New businesses:

Typically, the organic growth of your business will, by its nature, create an ideal ramp. Since transactional email is usually dependent on the number of users you have, the growth in your customer base will create a nice, comfortable growth curve in your email volume.

Maintain ip address warm up across ALL ISPs

Now that you’ve seen some sample schedules, it’s important to remember that you must maintain a steady volume during the entire warm up period at EACH ISP. (i.e. Split up your warm up schedule so each ISP is receiving a comparable amount of mail each day—don’t warm up Gmail on Monday, Yahoo! on Tuesday, etc.—evenly disperse your mail to each ISP on each day of warm up.) If not, your sending activity looks sporadic and you won’t be able to build a solid reputation.

What to Expect?

Once you begin warming up your IPs you can expect some bulking and blocking to occur. It is key to stick with the plan. Below are details of what you can expect and actions to take.

  • Bulking at Yahoo, AOL, Gmail. Typically clears up after a few sends with solid positive metrics, but it can take time to get inbox delivery. The key is to keep sending to engaged subscribers.
  • Delays at AOL, Microsoft and Comcast. The delays (421 bounces) will retry for 72 hours and if not delivered will bounce as a 5XX with the original 421 error in the bounce record. Delays are normal, and will lessen each day as reputation develops. As long as they are ultimately delivering there is no concern. However if they are timing out in large quantities you should back down your volumes to that ISP by tightening up your engagement
  • Possible blocking by ISPs can occur if the list isn’t engaged enough. The key is to segment carefully and tighten up engagement Again the key is to keep sending.
  • It is important to monitor your metrics and adjust the plan accordingly during the Warm-up period.

Why don’t other ESPs require IP address warmup?

Many other email service providers do not offer dedicated IP addresses to their customers – they place all of their customers on shared IP groups by default.

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


IP warming isn’t for everybody but hopefully this post has helped you work out if it is something you should be doing when setting up new email marketing platforms. A similar approach can also be used when wanting to ramp up the volume of emails you are sending in a way that won’t impact delivery rates. Email marketing can be such a powerful way to interact with your customers so ensuring your emails reach their recipients is as important as the content itself.


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