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How warm-up works

A new sending domain starts at 100 emails a day and ramps up over 30 days, so mailbox providers learn to trust it.

Overview

Section titled “Overview”

Mailbox providers like Gmail and Outlook are wary of a domain that suddenly starts sending lots of email. Warm-up builds your new sending domain’s reputation gradually: a daily limit that rises over your first month of live sending. Emails over the day’s limit aren’t dropped — they wait and go out the next day.

Warm-up is always on and can’t be skipped.

The schedule

Section titled “The schedule”

Warm-up counts days from the day live sending started on your domain: that day is day 1. Days run midnight to midnight, UTC.

Days since going live Daily limit
1–7 100 emails
8–14 250 emails
15–21 500 emails
22–30 1,000 emails
31 onward No daily limit

From day 31 the other deliverability controls still apply. See Sending limits and auto-pause.

When you go over the limit

Section titled “When you go over the limit”
  • The send returns queued_warmup (Queued (warm-up)) to the workflow straight away. The email is not lost.
  • It goes out after midnight UTC, oldest first, and counts toward the new day’s limit. If the new day’s limit fills up first, it waits another day.
  • When it goes out, it appears as Sent on the contact’s timeline. The workflow isn’t notified a second time, so don’t resend it. If it can’t be sent after all — the address was suppressed in the meantime, say — the reason shows in the Send log only.
  • It keeps its place in your email allowance while it waits, so it can’t be refused the next day for lack of allowance. If it ends up not being sent, the email is given back.

App Home’s Sending status shows the warm-up day, how many emails you’ve sent today out of the limit, and how many are queued for tomorrow.

Things to know

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  • Sandbox sends don’t warm up. Warm-up starts when you go live on your own domain.
  • A new domain starts over. If you remove your sending domain and add a different one, warm-up restarts at day 1 on the day the new domain goes live.
  • Plan ahead for big sends. If you send more than the daily limit every day, the queue keeps growing and emails go out later and later. When you’re moving existing volume — say, 2,000 receipts a day — onto Transactional Email, go live and ramp up before you need full volume.
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