Domain Warmup for Gmail – How to Improve Deliverability Step by Step

If you are sending mailings to a large number of Gmail recipients and notice an unusually high number of bounces or delivery errors, the cause is often a so-called rate limit imposed by Gmail. In this article, you will learn what is behind this, how to warm up your sending domain in a targeted way, and how to implement the process in MAILINGWORK.

What is a Gmail Rate Limit?

Gmail protects its users from spam by temporarily throttling unknown or insufficiently established sending domains when higher sending volumes are detected. A typical error message looks like this:

421 4.7.28 Gmail has detected an unusual rate of mail originating from your DKIM / SPF domain. To protect our users from spam, mail sent from your domain has been temporarily rate limited.

This means: Gmail has detected that your sending domain has not yet built up a sufficiently established reputation and is temporarily throttling incoming mail from it. Google has been enforcing this behaviour much more strictly recently – particularly for domains that have not yet been sending regularly to Gmail addresses.

Step 1: Check Technical Requirements

First, make sure that SPF, DKIM and DMARC are correctly configured for your sending domain – this is a fundamental requirement for Gmail to classify your domain as trustworthy. Without these records, the warm-up will be significantly more difficult.

Step 2: Register Your Sending Domain in Google Postmaster Tools

As a next step, we recommend registering your sending domain in Google Postmaster Tools. The tool gives you insight into:

the spam rate of your domain within the Google ecosystem
the delivery rate of your emails to Gmail addresses
your domain's overall reputation with Google

Registering your domain also sends a positive signal to Google and is an important first step in building your sender reputation.

You can find step-by-step instructions on how to set up Google Postmaster Tools here.

Step 3: Carry Out a Targeted Domain Warm-Up

To improve deliverability with Gmail in the long term, you should carry out a targeted domain warm-up for Gmail recipients.

The principle: start with a low sending volume and double it every two days – provided that the spam rate and delivery rates in Postmaster Tools are developing positively.

A recommended schedule as a starting point:

Day	Email Volume
1	50
2	50
3	100
4	100
5	200
6	200
7	400
8	400
9	800
10	800
...	× 2 every 2 days

Important: The volume should not be sent all at once, but spread evenly throughout the day. For example, 200 emails should not be sent at 9:00 AM in one go, but rather 50 emails each at 9:00 AM, 11:00 AM, 2:00 PM, and 4:00 PM. This appears more organic to Gmail and significantly reduces the risk of being throttled again.

Within MAILINGWORK, this throttling can be implemented using the sending throttle feature.

Open the desired mailing, go to the Sending tab, navigate to the Advanced section, and activate the sending throttle.

Which Recipients Are Suitable for the Warm-Up?

A good starting point for the warm-up is recipients who most recently returned a bounce – filtered to Gmail addresses using a target group. This way, you reach exactly the contacts that were previously affected by the rate limit, while at the same time building up a targeted reputation with Gmail.

Keeping an Eye on the Spam Rate

The spam rate in Google Postmaster Tools indicates how many of your emails were marked as spam by Gmail users – either manually via the "Report spam" button or automatically by Google's filters. The value is calculated as a percentage of delivered emails and shows you how trustworthy your sending domain is perceived to be by Gmail. A low spam rate signals to Google that your recipients consider your emails relevant and welcome – which sustainably strengthens your domain's reputation. If the value rises, Google interprets this as an indication of unwanted content and throttles the deliverability of your emails accordingly.

Throughout the entire warm-up process, the spam rate should remain permanently below 0.1%. Google Postmaster Tools displays this value directly. If the spam rate exceeds this threshold, the sending volume should not be increased further until the values have stabilised again.

Duration of the Domain Warm-Up

With consistent implementation and stable metrics in Postmaster Tools, you should expect a period of approximately 3–4 weeks until full deliverability with Gmail is achieved. This timeframe may be extended if the spam rate rises in the meantime or if the sending volume is increased too quickly – in such cases, it is better to take a step back and temporarily reduce the volume until the values have stabilised again.

How quickly you see progress also depends on the quality of your recipient list: active contacts who regularly open your emails and do not mark them as spam will significantly accelerate the reputation-building process. It is therefore worthwhile to start the warm-up with your most engaged Gmail recipients – that is, contacts who have recently interacted with your mailings.

Still Have Questions?

The domain warm-up requires some patience, but it is the most effective way to improve deliverability with Gmail in the long term. If you are unsure how to implement the process in MAILINGWORK, or if you have questions about your metrics in Postmaster Tools, our service team is happy to help.