What Is IP Warming and How to Do It Right

Why IP Warming Is Necessary

When you get a new dedicated IP address from your email provider (or switch providers, which means new IPs), that IP has zero reputation. ISPs have no data on it. They do not know if it belongs to a legitimate business or a spammer. Their default behavior is to be cautious: they accept small volumes but throttle or filter larger sends until the IP proves itself.

If you skip warming and send 50,000 emails from a brand-new IP on day one, ISPs will almost certainly block or spam-filter most of those emails. The spike in volume from an unknown sender looks exactly like what spammers do when they burn through new IPs. Even if your content is great and your list is clean, the volume pattern alone triggers protective filtering.

Warming applies primarily to dedicated IPs. If you are on shared IPs (common with smaller email providers), the IP is already warm because other senders on the same IP are establishing its reputation. However, your domain reputation still matters, so domain warming applies even on shared IPs.

IP Warming Schedule

A typical warming schedule runs 2-4 weeks depending on your target volume. Here is a conservative schedule for reaching 50,000 emails per day:

• Day 1-2: 50 emails per day. Send only to your most engaged subscribers (opened or clicked in the last 30 days).
• Day 3-4: 100 emails per day.
• Day 5-6: 250 emails per day.
• Day 7-8: 500 emails per day.
• Day 9-10: 1,000 emails per day.
• Day 11-12: 2,500 emails per day.
• Day 13-14: 5,000 emails per day.
• Day 15-17: 10,000 emails per day. Start mixing in moderately engaged subscribers.
• Day 18-21: 25,000 emails per day.
• Day 22+: 50,000 emails per day. Full list sending.

Roughly double your volume every 2 days. If you see bounce rates above 2% or spam complaints above 0.1% at any step, pause at that volume for an extra day or two before increasing. These are signals that you are moving too fast.

Rules for Successful IP Warming

Start With Your Best Subscribers

During the first week, only send to people who have opened or clicked your emails in the last 30 days. These subscribers are most likely to open, click, and not report spam, which sends positive signals to ISPs. As you ramp up, expand to 60-day actives, then 90-day, and only include your full list once you have reached higher volumes.

Send Every Day

Consistency is important during warming. Sending 500 emails every day for a week builds more reputation than sending 3,500 on one day and nothing for six days. ISPs look at sending patterns, and regular daily volume is a sign of a legitimate sender.

Monitor Metrics at Every Step

Watch these metrics daily during warming:

• Bounce rate: Should stay below 2%. Higher means list quality issues.
• Complaint rate: Should stay below 0.1%. Higher means you are mailing people who do not want your email.
• Open rate: Should be higher than normal since you are sending to engaged subscribers first. A drop may indicate spam folder placement.
• Deferrals (421 errors): Some deferrals are normal during warming. They mean the ISP is accepting your email slowly. Excessive deferrals mean you need to slow down.

Do Not Change Content During Warming

Send your normal email content during the warming period. Do not use special "warming" content that is different from what you will normally send. ISPs build a content profile for your IP, and suddenly switching to different content after warming can trigger new filtering.

When Warming Goes Wrong

Blocklisted During Warming

If your IP gets blocklisted during warming, stop sending immediately. Identify the cause (usually a high bounce rate from bad list data), fix the issue, request delisting, and restart the warming process from the beginning at lower volumes.

Consistently Low Open Rates

If open rates are significantly lower than expected during warming (under 10% when sending to engaged subscribers), your emails may be going to spam despite being delivered. Check sender reputation tools and verify your authentication setup.

ISP-Specific Problems

Sometimes warming goes well with Gmail but poorly with Outlook, or vice versa. Each ISP evaluates reputation independently. If one ISP is problematic, reduce volume specifically to that ISP while continuing normal warming with others. The ISP volume shaping guide covers how to manage per-ISP sending rates.