Domain warm-up and reputation: Stretch before you send

Domain reputation is important, but how do you go about building it? A proper domain warm-up will get you set on the right track to the inbox. Read more...

So, you wanted to send out a lot of emails but found that when you did, a lot of them either ended up undelivered or in the spam folder.

Think of it like this: When you start working out, you want to make sure that you stretch and warm up properly so that you don’t injure yourself. The same is true for when you start sending emails. An excellent warm-up process is needed to ensure that you don’t overdo it and damage your reputation.

What is a warm-up process?

You might already be familiar with the need for warming up a new IP, and domains are much in the same. Still, it’s important to note that both reputations are important considering that IPs and domains build and maintain separate reputations. 

A good warm-up period ensures that your IP and domain both build reputations with mailbox providers, which increases your chances of delivering to their inbox.

While the warm-up process can seem slow and tedious, it’s vital if you want to avoid the dreaded spam folder. Otherwise, you’ll start to experience other issues like throttling, greylisting, or outright blocking of your messages.

When we talk about the warm-up process, we talk about two major forms of warm-up: IP warm-up and domain warm-up. Depending on your current scenario and warmup needs, you will want to look at doing one or both of these.

Different warm-up scenarios

Established domain, new IP

In one scenario, you already have an established mail stream and domain. However, you’re looking to increase your sending and will require a second dedicated IP to share the load of that sending. 

This is where IP warm-up comes in: a new dedicated IP will be “cold.” In other words, the IP hasn’t seen traffic for a certain amount of time, and will not have a reputation attached to it. To build up this reputation, you need to warm up the IP. You can do this one of two ways: Manually or automatically.

When you warm up manually, you set hourly/daily sending limits in your system and slowly ramp up as you go. Alternatively, you can use Mailgun’s automated IP warm-up which takes that work off your hands.

New domain, established IP

Another scenario could be that you are adding in a new domain to handle a new type of messages you want to send out. Volume-wise, you are still well within recommended limits for your current amount of IPs, but want to build better domain reputations with more concise sending domains (,, etc.). 

Here is where many senders would say, “Well, my IP is already warm and has a good reputation, so I can just start sending at volume day 1.” While this is technically true, you could run the risk of your domain getting assigned a poor domain reputation due to its newness. In doing so, you endanger your overall deliverability.

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New domain and new IP

Lastly, you might have a scenario when domain and IP are both new and need warming up. In this case, you will want to warm them up in tandem with each other. Generally, this means that you forego the automated IP warm-up in favor of a manual warmup that benefits both the IP and the domain. 

The manual warm-up process will generally look the same for IP and domain warm-ups in term of the daily sending limits. Here’s a snippet of a warmup plan:

It’s especially important to note here that a plan with daily limits like this assumes daily sending. For example, you send days 1-5, then do not send on days 6 and 7, you cannot pick back up with the limit for day 8. Don’t rush it — slow and steady wins the race! 

The daily send numbers can also vary based on multiple factors such as list hygiene and engagement. Your sending needs to be monitored during the warm-up process so that changes can be made as necessary if you see a high rate of errors or your emails consistently go to the spam folder. 

Not all mailbox providers are created equal, and the same is true for warm-up plans. In some cases, you might want to develop and follow a more targeted warm-up plan for messages going to a specific mailbox provider. Targeted warm-up plans ensure that you meet their criteria - as much as they are known - to build reputation and land in the inbox. This can mean lower hourly and daily quotas, slower ramping, or spreading your traffic out over more time.

The DKIM factor and engaged recipients

It’s important to note that domain reputation is generally tied to the DKIM authority domain. By default, domains created within Mailgun are created with their own DKIM authority. This means that subdomains do not inherit and share a reputation with their parent domain unless specified during domain creation.

With a new domain, whether it’s a subdomain or a root domain, you’ll most likely need to warm up of the domain itself. This is done almost the same way as the manual IP warm-up. You start by limiting the volume going out of the domain every day and ramping this up slowly over time. 

Warm-up tip: Engaged recipients

Also, we recommend targeting your most engaged recipients during the warm-up process to ensure that you see good open and click rates. Sending to engaged recipients is a huge boost to reputation, and for some mailbox providers like Gmail, it is especially important. Gmail uses engagements as one of its main metrics to determine mailbox placement. Every little bit helps, right? Regardless, it’s worth asking...

Did the warm-up work?

Having gone through all of the warm-up exercises and stretches, you’ll ask yourself this — was it successful? The answer is largely going to lie in your event logs. You will want to keep an eye on failed events and their error messages, as well as your engagement numbers, for signs of success/failure.

Tools like Google Postmaster Tools help you monitor your IP and domain reputation specifically how Google sees it, so this might be a great solution for you if you’re only sending to Gmail. 

As with anything in life, there are no guarantees that following a set warm-up plan will net you 100% delivery and great deliverability. However, if you execute your warmup correctly, it should get you off to a good start and give you a foundation to build on further.

Need some extra help with your sending? Mailgun’s Deliverability service can assist you with building this foundation, by working with you to develop the warm-up plan that works best for you and your goals and providing advice along the way.

Learn about our Deliverability Services

Deliverability Services

Looking to send a high volume of emails? Our email experts can supercharge your email performance. See how we've helped companies like Lyft, Shopify, Github increase their email delivery rates to an average of 97%.

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