IP Warm-Up Recommendations
Why new sending IPs must be warmed up, what to expect, and a concrete ramp-up schedule (volume, pacing, audience selection).
What this document assumes
These recommendations assume you are sending wanted and expected email. With unwanted or unexpected email, these recommendations may actually hurt your deliverability compared to other strategies. For more on why, read Two Worlds of Email Deliverability.
Why a warm-up is required
When an IP address has not previously sent email, it must be "warmed up": you gradually increase volume and build credibility — a reputation with mailbox providers that you send good email from that IP address.
This is required because ISPs are very suspicious of email from a new IP address. 99 times out of 100, when a new IP address starts sending email, it is a spammer that was blocked on one IP and is moving to another. At the start of a warm-up, your reputation is not neutral but actually slightly negative.
Mailbox providers also apply throttles that limit the amount of email accepted from an IP address. Because of this, you must start by sending a small amount of email, establish a good reputation at that volume, and then gradually increase.
What to expect
You will not get your best deliverability at the beginning of a warm-up. In practice, roughly 75% of the time the very first campaign on a new IP address goes to the Spam folder at Gmail.
If your early campaigns are going to the Spam folder, don't worry — this is normal. If you are sending good email, the mailbox providers will figure it out.
What to do
1. Determine the number of IP addresses and segmentation strategy
See Basic IP Allocation and Advanced IP Segmentation and Allocation.
Put transactional email on its own IP address, separate from marketing email.
If you are using multiple IP addresses, only start sending on three IP addresses at the beginning of the warm-up, then add a new IP address every three days. If too many IP addresses start sending mail at the same time, this looks very suspicious to mailbox providers.
2. Ramp up volume, but start with your best data
- Start at about 5,000 messages per day from each IP address to each mailbox provider. The largest provider is typically about 25% of a typical mailing list, so this works out to roughly 20,000 messages per day per IP address overall.
- Increase this volume by 50% each week, as long as:
- There is no push-back from the mailbox providers (no high deferral or failure rates).
- You have been sending regularly. If you stop sending for a week, that time does not count toward your warm-up.
- Start with recipients who have recently clicked or opened an email from you — put your best foot forward. Mailbox providers are naturally suspicious of new IPs; overcome that suspicion with your best content and most engaged recipients.
- If your pool of recent clickers and openers cannot support 20,000 messages/day (or 5,000/day per provider) on each new IP, reduce the number of IP addresses to keep the per-IP volume healthy.
Provenance and how this compares to other authorities. The specific numbers above (≈5,000/day/provider start, +50%/week, three initial IPs, add one every three days, ≈75% of first campaigns to Gmail Spam) originate from a single vendor source (GreenArrow) and predate the Gmail and Yahoo bulk-sender requirements that took effect in February 2024 — note that the 5,000/day/provider starting point sits right at Gmail's 5,000-messages-per-day "bulk sender" threshold, so a warm-up at that volume must already satisfy authentication (SPF, DKIM, DMARC), one-click list-unsubscribe, and the <0.3% spam-rate ceiling from day one. Other authorities agree on the shape of a warm-up but differ on the numbers:
- AWS SES advises establishing a positive reputation over roughly two to six weeks per provider, sending to your most engaged users first, and settling around ~1,000 messages/day per provider to maintain reputation; its automatic warm-up ramps over 45 days independent of volume. (docs)
- Twilio SendGrid recommends starting far lower — on the order of ~50 messages on day one — and roughly doubling each sending day until you reach your target, typically over 4–6 weeks. (docs)
Treat the GreenArrow figures as one reasonable schedule on the more aggressive end, not a universal constant. Validate the starting volume and weekly step against your ESP's current guidance and against live inbox-placement monitoring, and back off if you see deferrals or Spam-folder placement.
3. Throttle the speed of your sending
Throttle the rate at which mail is injected into your MTA. During warm-up, each day's sending should be spread over at least four hours; if possible, spread it over eight hours — although not every business can do this.
Most sending platforms and MTAs offer a campaign speed or injection-rate setting for this (e.g., sending 20,000 messages at 5,000/hour spreads delivery over four hours). As the warm-up progresses, this speed can be increased.
4. Monitor inbox placement
Use an inbox-placement / seed-list monitoring tool for all campaigns during the warm-up period. This provides valuable data on whether mail is reaching the Inbox or the Spam folder at each provider, which drives decisions about when to increase volume.