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Domain warm-up

A brand-new sending subdomain has no reputation with mailbox providers. If it suddenly sends thousands of emails on day one, Gmail, Outlook, and the rest read that as spammer behavior: mail gets throttled or lands in the spam folder. Warm-up prevents this by capping how much you can send per day and raising that cap on a schedule, so providers see a natural, steadily growing sender.

Warm-up is on by default for every new promotional sending domain. You do not need to do anything to benefit from it.

How the ramp works​

The daily cap starts small and grows by a percentage every few days. By default it starts at 100 emails per day and doubles every 2 days, until it reaches the cap ceiling. Once the cap reaches the ceiling (or the maximum warm-up period elapses), the domain graduates: warm-up stops limiting anything and the domain sends at full volume from then on.

Crucially, mail over the cap is never dropped. If a campaign is bigger than today's remaining allowance, the overflow simply drips to the next day and continues until everything is sent. Automations behave the same way: a step that hits the cap is deferred, not skipped.

The warm-up card​

The Domain warm-up card appears under your promotional stream on the Sending Domains page once the domain is verified. While the domain is warming, it shows:

  • The current position in the ramp: Day and Step.
  • Today's progress: how many emails have been sent against today's cap, with a progress bar.
  • The estimated graduation date ("Graduates ~...").

Once the ramp completes, the card shows a Graduated badge and confirms that nothing is being throttled anymore.

Tuning the ramp​

While a domain is warming, the card exposes the schedule so you can adjust it:

  1. Open Domains → Sending Domains and find the warm-up card under the promotional stream.
  2. Edit any of the fields: Start / day (the initial daily cap), Growth % (how much the cap grows per step), Every (days) (how many days each step lasts), and Cap ceiling (the cap at which the domain graduates).
  3. Click Save.

A slower ramp (lower growth, longer steps) is safer for lists with unknown engagement; the default is a sensible middle ground for a clean, opted-in list.

Turning warm-up off​

The On / Off toggle at the top of the card disables warm-up entirely. With warm-up off, campaigns send at full volume immediately.

If the domain has already graduated, the toggle just flips, since warm-up is not limiting anything anyway. If the domain is still actively warming, SmartMailing asks you to confirm first: on a new subdomain with no reputation, sending at full volume risks spam-foldering and provider throttling.

tip

Only disable warm-up for a domain that already has an established sending history. If you migrated an active domain from another provider and it has been sending steady volume for months, skipping the ramp is reasonable. For anything genuinely new, let the ramp run.