IP and Domain Warm-Up
Updated over a week ago

When you start sending emails from a brand new domain or infrastructure, there’s no history of sending from your new IP; this means that Internet Service Providers (ISPs) have no way of judging your sender reputation, yet. When this happens, the domain is treated as a fresh sender.

  • A sender reputation is a score that an ISP assigns to an organization that sends email (it's a crucial component of your email deliverability).

When ISPs are suspicious about emails coming from a new or "cold" IP address, they might:

  • Put that message in spam

  • Rate limit, or throttle, the amount of email accepted from a particular sender during a specific period. If senders try to send an email above that acceptable threshold, the ISP will reject your email, resulting in higher bounces back or deferrals.

Different mailbox providers might place emphasis on different areas; for example, Gmail places a greater emphasis on sending domain while Microsoft is primarily IP reputation.


“Warm up” is the process of slowly & gradually increasing your email volume over a few weeks in order to establish a positive sending reputation with mailbox providers.


Since ISPs treat email volume as a key determining factor when detecting spam, it is best to begin sending a low to moderate volume, eventually working your way up to larger volumes. The best way to do this is through your most engaged audiences. These audiences help garner positive engagement on the emails, which in turn tells mailbox providers that the emails are relevant and wanted by the subscribers.

Begin with the most active and engaged users, gradually expanding the audience. An active & engaged subscriber could be someone who has opened or clicked an email in the past 7/15/30/60/90/120/180 days respectively, or who has recently purchased from you.

A 4 to 6 week schedule is the minimum for warm up. Based on your database size, we might need to warm up for 6 to 8 weeks.

During the warm-up phase, the more consistent you are with volume & frequency, the faster you will establish a positive sending reputation. If you send infrequently – anything less than weekly – it will take more time to build a positive sender reputation.


  • Creatives: Use a different creative for each send. Don’t send the same creative to the same audience. The key is to send fresh & engaging content to drive positive engagement metrics.

  • Consistency: Maintain a consistent sending frequency. Don’t miss a warm-up send and if there’s a change in your sending schedule, resume from where you left off. Don’t increment the send volume significantly.

  • Key KPIs: It’s important to keep track of engagement metrics like unique open rates, hard & soft bounce rates, spam rates, and unsubscribe rates.

    • NOTE: Your Gmail reputation is only published after a couple of initial sends.

  • Suppress your sends at other ESPs: On days when you are scheduled to send from Bluecore, suppress the warm-up audiences at your other ESP so there’s no double-mailing to the same audience.

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