How to warm up a new sending domain

Mailbox providers decide how much of your mail to accept, and where to file it, partly from your domain's sending history. A domain you verified last week has none. Warming it up means building that history on purpose: small sends to people who want the mail, then more volume once those sends land well.

Why a new domain gets throttled

Gmail's email sender guidelines say it tracks volume, feedback and limits per domain and per IP address, and that DKIM and SPF quotas are specific to your domain. Sending through a provider with well-established shared IPs doesn't change that. The IP has a history; your domain doesn't.

A domain with no history that suddenly sends hundreds or thousands of messages looks like a compromised account or a bulk spammer. The usual first response is a temporary rate limit. The Gmail SMTP error reference lists 421 4.7.28 as Gmail detecting an unusual rate of mail and limiting it to protect its users. If the mail also looks unwanted, Gmail can refuse it with 550 5.7.1, which it uses for messages it considers likely unsolicited.

This doesn't take a huge list. A campaign to a few hundred recipients from a young domain, followed shortly by a second one, can see a large share of its Gmail mail throttled or rejected with exactly those two codes.

What mailbox providers publish

No major mailbox provider publishes a warm-up schedule. Gmail's sender guidelines come closest, and their advice on increasing volume reduces to this:

• Start with a low volume to engaged users and increase it slowly over time.
• The more mail you send, the more slowly you should increase volume.
• You can increase faster when you send daily instead of weekly.
• Send at a consistent rate and avoid bursts.
• Avoid sudden volume spikes if you have no history of sending large volumes.
• Monitor delivery in Postmaster Tools while you increase volume.
• If messages start bouncing or being deferred, reduce volume until the error rate drops.

Yahoo's sender best practices and Microsoft's Outlook.com sender policies cover authentication, unsubscribes and list hygiene, and give no ramp either. Any day-by-day warm-up table you find online is someone's opinion. That includes the ramp in this guide.

Before the first send

Fix authentication before you send anything. Mail that fails authentication builds the wrong kind of history.

• SPF or DKIM must pass, and ideally both. Gmail requires every sender to authenticate with at least one of them, and rate limits or blocks mail that passes neither (421 4.7.26, 550 5.7.26). If a check fails, see SPF record not found or DKIM verification failing.
• Publish a DMARC record. A policy of p=none is enough to start.
• Add the domain to Google Postmaster Tools. You verify it with a DNS TXT or CNAME record. Google notes that data can be missing on days with too few messages, so set it up now and it will be reporting by the time your volume is meaningful.
• Pick the From address and domain for each kind of mail and keep them stable. Gmail asks that messages of the same category use the same From address, and after significant changes to your sending infrastructure or headers it advises ramping up the changed traffic separately.

A minimal DMARC record looks like this:

_dmarc.yourdomain.com.  TXT  "v=DMARC1; p=none; rua=mailto:dmarc-reports@yourdomain.com"

Plan for the bulk-sender line, too. Gmail's requirements for senders of 5,000 or more messages a day to personal Gmail accounts include DMARC and one-click unsubscribe on marketing mail, and a sender who crosses that line once is treated as a bulk sender permanently. Outlook.com has enforced SPF, DKIM and DMARC for domains sending more than 5,000 messages a day since May 5, 2025. A successful warm-up can take you past both. The full list is in bulk sender requirements for Gmail, Yahoo and Microsoft.

A conservative ramp

What follows is our guidance. No mailbox provider endorses a specific schedule.

1. On day one, send a few hundred messages to your most engaged contacts: people who signed up, opened or clicked recently.
2. Grow the next day's volume only if the previous day's sends finished cleanly, with almost no bounces, no spam reports and no deferrals. Never more than double from one day to the next.
3. Reach your normal daily volume over about a week. A larger list needs a slower climb, in line with Gmail's point that the more you send, the more slowly you should increase.
4. Add less engaged contacts last, once the domain handles its normal volume without trouble.

Old, unengaged addresses are the ones most likely to bounce or report you, so they belong at the end of the ramp, or nowhere. Email list hygiene covers how to decide which to keep.

Within each day, spread the volume where you can. Gmail asks for a consistent rate, so several smaller batches across the day are safer than one large burst.

Signals to watch during the ramp

• A 421 4.7.28 deferral from Gmail means you are sending faster than your domain's history supports. Stop growing and drop back to the last volume that went out cleanly.
• A policy rejection such as 550 5.7.1 or 550 5.7.28 usually means Gmail judged the mail unwanted. Pause and review who you are mailing before the next send.
• A high hard-bounce rate on the first sends usually means the list is old or wasn't collected with consent.
• Postmaster Tools shows the user-reported spam rate for mail to personal Gmail accounts. Gmail asks senders to keep it below 0.1% and never reach 0.3%.

For what each code means and what to do about it, see email bounce codes explained.

Microsoft's SNDS reports per IP and only to whoever is responsible for that IP, so it helps only if you send from IPs you control. Yahoo's Complaint Feedback Loop sends you copies of spam reports on DKIM-signed mail, which is worth setting up before your volume grows.

If you get throttled

A rate limit is temporary, and deferred messages are retried. Don't add the next campaign on top of it. Google's advice for servers that hit 4.7.28 is to stop sending for at least 10 minutes, then resume over a single connection and add connections gradually. If you send through an email service provider, its retry logic handles that part.

What you control is volume. Cut back to the last level that went out without errors, hold there for a day or two, then grow again in smaller steps than before. If you saw policy rejections or a spam rate approaching 0.3%, a slower ramp won't be enough: follow how to recover a damaged sender reputation.

Warm-up isn't only for new domains

Any jump well past your usual volume carries the same risk, whether it's a list you haven't mailed in months or a send several times larger than a normal day. Split a send far larger than usual into a few sends over several days, with the most engaged recipients first. Spacing those sends also matters for the people on the list; how often to send marketing email covers cadence.