Mailbox providers judge a sender by its history. A domain registered last week, sending its first thousand emails, has none, and that blank record looks exactly like the start of a spam run. Warming up means sending gradually, to people who want your mail, so providers learn that you are a legitimate sender before you ask them to trust you with volume.
This applies whether you use a new domain, a new sending subdomain, or a new mail server.
Why warm-up exists
Providers cannot read your intentions. They infer them from patterns: how fast your volume grows, how many messages bounce, how many recipients open, reply or complain. A steady, modest, well-received start produces good data. A sudden spike of unfamiliar mail to cold addresses produces bad data, and bad first impressions are hard to undo.
Before you send the first message
Warming up with broken foundations wastes effort. Check these first:
- Authentication is complete. SPF, DKIM and DMARC all pass, with the From domain aligned. Confirm with the header test.
- The domain looks real. It has a working website, a contact address, and the usual
abuse@andpostmaster@aliases. - Replies work. Use a real From address people can answer, and not a no-reply address, at least for your first messages. Replies are one of the strongest positive signals.
- Your list is clean. Only addresses that gave you permission, ideally recently.
A practical ramp
Numbers vary by provider, so treat this as a shape, not a rule. Move up only if the previous step went well, with few bounces and no complaints.
| Day | Messages per day | Who to send to |
|---|---|---|
| 1 to 3 | 20 to 50 | Your most engaged contacts, colleagues, customers who know you |
| 4 to 7 | 100 to 200 | Recent customers and sign-ups |
| 8 to 14 | 300 to 800 | Active users |
| 15 to 21 | 1,000 to 3,000 | Wider list in small batches |
| 22+ | Increase by about 25 to 50% a step | Everyone who opted in |
Spread each day's sends over several hours instead of one burst. Mix providers: if all your early mail goes to one provider, you build reputation only there.
Transactional mail warms up differently
Password resets, receipts and verification codes arrive when someone is waiting, and recipients open them within seconds. That strong engagement is a gift. If your product sends these, they will build a positive record faster than newsletters. Start your warm-up with this real traffic rather than synthetic tests, and give it its own subdomain so a later marketing mistake cannot touch it.
What to watch while you ramp up
- Bounce rate. Keep it under about 2%. Permanent failures (5xx codes) mean the address does not exist. Remove them immediately. See bounces and SMTP error codes.
- Complaints. Aim for far under 0.1%. If complaints appear, stop increasing and look at who you are sending to.
- Deferrals. Temporary 4xx rejections such as Gmail's "unusual rate of mail" mean you are going too fast. Back off to the previous step and wait.
- Postmaster data. Register the domain in Google Postmaster Tools and Microsoft SNDS, and look at spam rate and reputation as volume grows.
What not to do
- Do not buy a list or "warm-up" with scraped addresses. Spam traps and complaints will wreck the domain.
- Do not use fake engagement networks that open and reply to your mail automatically. Providers are good at detecting artificial patterns, and it teaches you nothing about real recipients.
- Do not change several things at once. New domain, new content, new list and new provider together make problems impossible to diagnose.
- Do not skip the gradual step because the first batch went well. One good day is not a track record.
Warming up a subdomain
You can start a new subdomain such as mail.yourdomain.com under a domain that already has a good name. Reputation is partly inherited from the parent, but providers also track subdomains separately, so the new stream still needs a measured start. It remains the best way to separate different kinds of mail.
How Mailions helps
Mailions sets up a dedicated DKIM key, SPF and DMARC records for each domain and verifies them before you send, which removes the biggest cause of poor first impressions. The sending log shows each message's relay result and the monthly recipient allowance keeps early volume modest. Warm-up itself is something only your sending behaviour can do, and inbox placement can never be guaranteed. If you want to talk through a launch plan, contact us.