Email Warmup

Email warmup is the practice of gradually increasing how much email you send from a new domain or IP address, so mailbox providers can build a reputation for it before you send at full volume. A new sending domain has no history. Google's sender guidelines say to start with a low volume to engaged users and increase slowly, because a sudden spike from a sender with no volume history can lead to rate limiting or a reputation drop.

When warmup matters

Warmup applies to new sending identities and to sudden changes in volume. You warm up when you move to a new domain or subdomain, when you start sending from a dedicated IP, or when your volume is about to jump well past what a provider has seen from you before. It matters most for cold or previously unused domains. A shared pool shares its IP reputation with every sender on it, but Google tracks volume and feedback per domain as well as per IP, so a new domain still needs its own ramp. Either way, set up SPF, DKIM, and DMARC before the first send. Google requires SPF or DKIM for all senders and all three for anyone sending 5,000 or more messages a day to Gmail.

How a warmup ramp works

A ramp starts small and grows in steps while the signals stay healthy. Send to your most engaged contacts first. Watch SMTP responses, bounce rate, spam-complaint rate, and domain reputation at each step. If messages start bouncing or being deferred, reduce volume until the error rate drops, then increase again slowly. Google's guidelines also say to send at a consistent rate rather than in bursts, and warn that suddenly doubling previous volume can trigger rate limiting or a reputation drop. See email deliverability for the metrics to track.

What not to do

Warmup is about earning a real reputation, so anything that fakes engagement works against it. Do not warm up by sending to purchased or scraped lists. They produce bounces and spam-trap hits that damage the domain you are trying to establish. Be wary of services that “warm up” an inbox by exchanging automated opens and replies between fake accounts. The engagement they create is not from your audience, so it tells a provider nothing about how your real recipients will respond. For the failure modes to avoid, see why emails go to spam.

Warmup at Loops

Loops manages sending infrastructure and volume shaping for SaaS teams, so transactional and marketing email send from one platform with the deliverability basics handled: domain setup, authentication, bounce handling, and suppression. A clean, opted-in list and steady sending are still what make a ramp healthy. See the email deliverability guide for the full checklist.

FAQ

What is email warmup?
Gradually increasing the volume you send from a new domain or IP so mailbox providers can build a reputation for it, instead of starting with a large, sudden send from a source they have never seen.

How long does warmup take?
There is no fixed number. The ramp is paced by the signals, not the calendar. Keep increasing while SMTP responses, bounce rate, spam rate, and domain reputation stay healthy, and reduce volume when they do not.

Do warmup services work?
Services that ramp volume to real, engaged recipients follow the same approach described above. Services that generate fake opens and replies between automated inboxes do not build a reputation based on your actual audience.

Related: Email deliverability, SPF, DKIM, DMARC.