What is Email Warmup? IP and Domain Warming
Email warmup is the practice of gradually increasing sending volume from a new IP address or domain over several weeks, starting with the most engaged recipients, so mailbox providers can build a positive reputation for it instead of throttling or filtering a sudden burst of mail from an unknown source.
Why new senders have to warm up
Mailbox providers judge incoming mail partly by the history of the IP address and the domain it comes from. A brand-new IP or domain has no history, and a sudden burst of volume from an unknown source is exactly what spam campaigns look like. So providers throttle it: they defer some messages with temporary 4xx errors, route some to spam, and watch how recipients react before trusting more.
What a warmup plan looks like
Start with a small daily volume and increase it gradually over two to six weeks, roughly doubling each step as long as the signals stay clean. The details matter more than the exact numbers:
- Send your most engaged mail first. Password resets, receipts and messages to recently active users get opened and rarely reported, which is the reputation you want to build.
- Keep volume steady. A consistent daily pattern builds trust faster than large, irregular batches.
- Watch the signals and pause if they turn. Rising deferrals, bounces or complaints mean hold the current volume until they settle.
IP warmup vs domain warmup
On a shared IP pool, the IPs are already warm and carry the reputation of every sender on them; what you still have to build is the reputation of your own sending domain. Providers increasingly weight domain reputation more heavily than IP reputation, so a new domain benefits from a gradual ramp even on warm IPs. A dedicated IP needs both.
Warm is not permanent
Reputation decays when an IP or domain goes quiet. A sender that stops for a few weeks and then resumes at full volume can see the same throttling as a new one, so ramp back up after long pauses too.
Frequently asked questions
How long does email warmup take?
Typically two to six weeks, depending on the target volume and how recipients respond. Increase volume in steps, roughly doubling while bounces, deferrals and complaints stay low, and hold the current level when they rise.
Do I need to warm up on a shared IP?
The shared IPs are already warm, but your sending domain still has its own reputation. A new domain benefits from ramping volume gradually and starting with engaged recipients, even on warm IPs.
What happens if I skip warmup?
Providers usually throttle unknown senders: messages are deferred with temporary 4xx errors, some are routed to spam, and a large first send can damage the reputation you were trying to build.