IP Warm-Up Recommendations

What these recommendations assume

The schedule below is built for senders whose recipients want and expect their mail. For mail that recipients did not ask for or do not recognize, applying it can leave your deliverability worse off than a different approach would. Two Worlds of Email Deliverability explains the reason.

Why a warm-up is required

A mailbox provider has no history for an IP address that has never sent mail, so it has no reason to trust it. Warming up means raising volume step by step until providers have seen enough good mail from the address to give it a reputation: the credibility that lets later campaigns through.

The starting point is worse than a blank slate. GreenArrow reports that 99 times out of 100, a newly active IP address belongs to a spammer who was blocked elsewhere and has moved on. Providers therefore treat a new address with deep suspicion, and your reputation begins slightly below neutral.

Providers also cap how much mail they will accept from a single IP address. The way through is to begin with small volumes, prove good behaviour at that level, and only then send more.

What to expect

Early campaigns will not show your best results. GreenArrow observes that in roughly 75% of cases, the first campaign sent from a new IP address is placed in the Gmail Spam folder.

Spam-folder placement in the first days is normal and no cause for alarm. Providers learn from how recipients respond, so good mail earns better placement as the warm-up continues.

What to do

1. Decide how many IP addresses to use and how to segment them

Basic IP Allocation and Advanced IP Segmentation and Allocation cover how many IP addresses to use and how to divide your mail between them.

Give transactional email a dedicated IP address instead of sharing one with marketing email.

When the warm-up involves several IP addresses, bring them online in stages: begin with three, and add one more every three days. A large group of addresses that all start sending on the same day is a pattern providers treat as highly suspicious.

2. Increase volume, but start with your best data

• Aim for roughly 5,000 messages a day from each IP address to each mailbox provider at first. Because the biggest provider usually holds about 25% of a list, that comes to about 20,000 messages per day per IP address in total.
• Raise the volume by 50% each week, provided that:
  • providers are accepting the mail without high rates of deferral or failure, and
  • your sending has been steady. A week with no sending does not count toward the warm-up.
• Send first to the recipients most likely to respond: those who recently clicked or opened one of your emails. Providers distrust new IP addresses by default, and your best content going to your most engaged recipients is the strongest answer to that distrust.
• When those recent clickers and openers cannot fill 20,000 messages a day (or 5,000 a day for each provider) on every new IP address, use fewer IP addresses, so that each one still carries a healthy volume.

How these figures compare with other sources. The specific figures above (a start of ≈5,000 a day for each provider, an increase of +50% a week, three IP addresses at first, one more every three days, and ≈75% of first campaigns in Gmail's Spam folder) come from a single vendor, GreenArrow. They also predate the bulk-sender requirements of Gmail and Yahoo that took effect in February 2024. The starting point of 5,000 a day for each provider sits exactly at Gmail's "bulk sender" threshold of 5,000-messages-per-day, so a warm-up at that volume must meet the requirements for authentication (SPF, DKIM, DMARC), one-click list-unsubscribe and a spam rate below the <0.3% ceiling from the first day. Other sources agree on the general shape of a warm-up but give different figures:

• AWS SES advises building a positive reputation over roughly two to six weeks for each provider, sending to your most engaged users first, and settling at around ~1,000 messages a day for each provider to maintain your reputation. Its automatic warm-up ramps up over 45 days, whatever the volume. (docs)
• Twilio SendGrid recommends starting far lower, at around ~50 messages on the first day, and roughly doubling the volume each sending day until you reach your target, which typically takes 4–6 weeks. (docs)

Treat the GreenArrow figures as one reasonable schedule, at the more aggressive end, not as a universal constant. Check the starting volume and the weekly increase against your ESP's current guidance and against live inbox placement monitoring, and slow down if you see deferrals or placement in the Spam folder.

3. Throttle the speed of your sending

Control how fast mail enters your MTA. While warming up, let each day's sending take at least four hours to go out, and eight hours where you can, although not every business can wait that long.

Most sending platforms and MTAs offer a campaign speed or injection rate setting for this (for example, sending 20,000 messages at 5,000 an hour spreads delivery over four hours). Raise the speed as the warm-up progresses.

4. Monitor inbox placement

Use an inbox placement or seed list monitoring tool for every campaign during the warm-up. It shows whether mail reaches the Inbox or the Spam folder at each provider, which tells you when to increase volume.

Related articles

• Basic IP Allocation
• Foundations of Email Deliverability
• Advanced IP Segmentation and Allocation