Key Considerations and Supplemental Information for IP Warming

What Is IP Warming?
IP warming is the process of gradually increasing send volume to improve the reputation score of an IP address that currently has a low or unrated reputation. For more information, see Reputation Warming for Email Studio

What Is an IP Reputation (Score)?
IP reputation is a system that evaluates the trustworthiness of a sending IP address and quantifies that trust as a numerical score. Each mailbox service provider (MSP) — such as Gmail, Yahoo Mail, mobile carriers, and ISPs — and the external reputation scoring services they reference may apply their own individual evaluation criteria.

Why Is IP Warming Necessary?
When an IP address has a low or unrated reputation score, receiving servers may block incoming messages or throttle delivery. Maintaining a sufficient reputation score is therefore essential for sustaining email deliverability.

About IP Warming Target Benchmarks
While the documentation referenced above outlines the specific steps to follow, the following questions come up frequently:

To verify whether warming has been completed successfully, use one of the following external reputation scoring services:

About the Timing of IP Warming
IP reputation does not only degrade during initial onboarding. It can also decline unexpectedly due to situations such as the following:

Regularly monitor the reputation scores listed above. If issues arise, be aware that re-warming may be required.
To reduce these risks, it is recommended to maintain good list hygiene practices — such as managing subscriber statuses and removing inactive subscribers (for example, those who have not opened an email over an extended period) from your send lists.

 

About Dedicated vs. Shared Sending IP Addresses
IP warming requires a sufficient number of active subscribers, as outlined in the documentation referenced above. However, depending on the nature and scale of your business, your send volume may not meet the minimum threshold required for warming.

In such cases, as described in the following document, using a shared sending IP address instead of a dedicated one is also an option:
Marketing Cloud Dedicated IP and Shared IP use policy

About Email Deliverability Considerations in Japan
The IP reputation and IP warming concepts described above are primarily used as evaluation criteria by Western ISPs such as Gmail, Outlook, and Apple Mail. However, Japan-specific mail services — such as Yahoo Mail Japan, domestic corporate ISPs, and mobile carriers — often apply their own proprietary evaluation criteria. In Japan, deliverability is frequently controlled by "the number of simultaneous sends per IP address" rather than IP reputation alone.

It is therefore essential to understand the domain distribution of your subscriber list (see note below) and determine what approach is most effective for ensuring deliverability — whether that means performing IP warming, increasing the number of IP addresses, or both.

Note: For example, if many of your subscribers use corporate domains, those domains may actually be running on services such as Google Workspace or Microsoft 365. In that case, they are subject to the same filtering controls as Gmail or Outlook respectively — which means IP warming is required.

Additional Information on Email Deliverability
For information on how to regularly check IP reputation status, refer to the following:
Marketing Cloud Deliverability Tools and Reports

For further context, the following services are commonly used:

For additional reference, see also:
Email Deliverability