Optimizing Email Deliverability: The Importance of Domain Warm-Up

Jan 31, 2024 | Blog

In the context of transactional emails, where timely and critical information is exchanged between businesses and users, ensuring deliverability is paramount.

Transactional emails, such as order confirmations, account notifications, and password resets, play a pivotal role in maintaining customer trust and engagement. This often leads to a large number of emails being sent from one domain, causing some email service providers (ESPs) to flag these as spam.

To optimize the deliverability of these essential messages, businesses must understand and implement a robust domain warm-up strategy tailored specifically for transactional email scenarios.

What is Domain Warm-Up

Domain warmup refers to the gradual process of establishing a positive reputation for a new email sending domain or IP address. This is particularly important because ESPs and spam filters often monitor the behavior of senders to determine whether their emails are legitimate or spam.

The domain warmup typically involves gradually increasing the volume of emails sent over a period of time. This allows the sender to prove to ESPs that they are a legitimate sender with valid and wanted content. The warmup process might include sending emails to a small, engaged audience initially, and then gradually increasing both the volume and the size of the recipient list.

Why Domain Warm-Up Matters

Transactional emails are often characterized by their urgency and importance. Whether it’s a purchase confirmation or a password reset, users expect these messages to reach their inboxes promptly.

However, launching a new domain or resuming email activities from an inactive one without proper warm-up can lead to deliverability challenges. ISPs (Intrusion Prevention System) may flag these sudden surges in email volume, potentially affecting the timely delivery of transactional emails.

Key Considerations for Domain Warm-Up

Identify Transactional Email Types

Different transactional emails may have varying levels of urgency. Categorize your transactional emails based on importance and urgency, as this will guide your warm-up strategy. For example, order confirmations might be considered more critical than routine account notifications.

Gradual Volume Scaling

Begin your domain warm-up with a small volume of transactional emails to your most engaged users. Focus on critical messages first and gradually increase the volume over time. This ensures that ISPs recognize your domain as a legitimate sender of time-sensitive information.

Prioritize Authentication

Implement robust email authentication mechanisms such as SPF, DKIM, and DMARC to authenticate your domain. Authentication not only boosts security but also instills confidence in ISPs that your transactional emails are legitimate and trustworthy. (link til de forskellige blogs)

Prioritize Authentication

Segment your user base based on their interaction history and preferences. Send transactional emails to different segments, tailoring content and frequency to match user expectations. This segmentation not only enhances deliverability but also contributes to a positive sender reputation.

Monitoring and Optimization

Constantly monitor the performance of your transactional emails during the warm-up process. Keep a close eye on delivery rates, open rates, and user interactions. If any issues arise, be prepared to adjust your warm-up strategy promptly.


When sending transactional emails, warm-up initiatives are not just a best practice but a strategic imperative.

The specific warmup plan can vary based on factors like the volume of emails you plan to send, the type of content, and the engagement levels of your recipients. The goal is to build trust with email providers and establish a positive sender reputation, reducing the likelihood of emails being marked as spam.

By carefully planning and implementing a warm-up strategy tailored to the unique characteristics of transactional emails, businesses can optimize deliverability, reliability, and user engagement. This will ensure that critical information reaches users when they need it the most, further encouraging trust and user satisfaction.

Heysender blog

Read our other blog entries to get new inspiration for your transactional emails.

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