Warming up an email domain is an essential process when you start sending from a new domain or when a domain has not been used (actively) for a long time. Mailbox providers such as Gmail, Microsoft, and Yahoo gradually build a reputation for your domain based on sending behavior and engagement.

During the warming process, the sending volume is increased step by step. You begin with small numbers of emails sent to your most engaged recipients and gradually increase the volume over several days or weeks. This allows mailbox providers to recognize the domain as trustworthy, significantly improving the likelihood of good inbox placement. Inactive recipients should be explicitly avoided during the warming phase.

Consequences of a poorly warmed email domain

When an email domain is not warmed up or is warmed up incorrectly, mailbox providers such as Gmail, Microsoft, and Yahoo form an impression of the sender’s reliability from the very first send. A sudden high sending volume from a domain without a reputation is often seen as suspicious behavior. In practice, this frequently results in messages landing in the spam folder or, in some cases, being temporarily blocked.

In addition, insufficient warming quickly leads to a negative domain reputation. Mailbox providers largely base their assessment on recipient engagement signals. When emails are sent too quickly to large, broad, or weakly engaged audiences, opens and clicks lag behind and the likelihood of spam complaints increases. Higher bounce rates may also occur due to less well-maintained data files. This combination of signals causes the domain to be classified as unreliable fairly quickly.

Another common consequence is that mailbox providers actively intervene in sending traffic. This may occur through throttling, where the number of allowed messages per time unit is limited, or through temporary blocks that result in soft bounces. This can delay campaigns and cause disruptions in both marketing and transactional communication.

What makes this particularly problematic is that reputation damage often does not recover quickly. Even when sending behavior is later improved, it can take weeks or months before mailbox providers rebuild their trust. In severe situations, deliverability may remain structurally poor, and it may even be necessary to start with an entirely new sending domain.

The impact is not only technical but also commercially noticeable. Poor inbox placement means less visibility, lower engagement, and ultimately fewer conversions. A careful warming process is therefore not an unnecessary step, but a fundamental requirement for sustainable email performance.

The domain is warmed up – what’s next?

When a domain has been successfully warmed up, it means mailbox providers have built sufficient trust in the sending behavior. The foundation for good inbox placement has been established, but this is not the endpoint. Especially after the warming process, it is important to actively maintain and further strengthen this trust.

Mailbox providers continue to evaluate sending behavior continuously. This means consistency in volume, frequency, and audience remains essential. Large fluctuations in sending volume, sudden spikes, or adding large numbers of less engaged contacts can still lead to a deterioration in reputation. Changes in content type or sending patterns can also raise renewed suspicion.

A warmed-up domain performs best when the sending profile grows gradually and in a controlled manner alongside the database and campaigns. By consistently focusing on relevant content, healthy engagement, and stable volumes, the reputation remains positive and strong deliverability results can be sustainably maintained.

Need help

A solid warm-up plan and accurate monitoring are essential when warming up a domain. The plan always differs per domain. Depending on the number of contacts and the desired email frequency, an appropriate plan must be created.