IP Warming: A Practical Schedule for New Dedicated Sending IPs

Why a Fresh IP Has No Reputation

A brand-new IP address is invisible to mailbox providers. It has no sending history, no complaint data, and no engagement record. When Gmail or Microsoft 365 sees mail arriving from an unknown IP, they treat it with suspicion—even if your domain authentication is perfect. The response is typically heavy filtering, deferral, or throttling until the IP accumulates enough legitimate sending history to establish a reputation.

IP warming is the process of building that reputation deliberately. You start with low volumes sent to your most engaged subscribers, then expand gradually over several weeks. Done correctly, mailbox providers see a pattern of consistent sending, low complaints, and strong engagement—all signals that the IP belongs to a legitimate sender.

Who Needs to Warm an IP

You need to warm an IP when:

• You're moving from a shared IP pool to a dedicated IP
• You're migrating from one ESP or relay to another
• You're spinning up a new sending domain or subdomain
• A previously dormant IP (no significant volume for 30+ days) is back in use

If you're on a shared IP, warming is handled by your provider—that's one of the advantages of shared infrastructure. The tradeoff is that you also share reputation with other senders on the pool. A dedicated IP gives you full control at the cost of having to establish your own reputation from scratch.

Pre-Warming Checklist

Never start warming until these are confirmed:

1. SPF record covers the new IP
2. DKIM is configured and signing is verified
3. DMARC is published (at minimum p=none)
4. Reverse DNS (PTR) record resolves to a valid hostname for the IP
5. The sending hostname doesn't appear on any major blocklists (check Spamhaus, Barracuda, SURBL)
6. Your list is clean—suppressed hard bounces, removed inactives

Warming a misconfigured IP is wasted effort. Fix authentication first.

A Practical Week-by-Week Warming Schedule

Volume targets below assume a healthy, engaged list. If your list is older or less engaged, be more conservative—cut these numbers in half and extend the schedule.

Week 1

• Day 1: 200 messages
• Day 2: 400 messages
• Day 3: 700 messages
• Day 4: 1,000 messages
• Day 5: 1,500 messages
• Days 6–7: rest (no sending)

Week 2

• Day 1: 2,500 messages
• Day 2: 4,000 messages
• Day 3: 6,000 messages
• Day 4: 9,000 messages
• Day 5: 12,000 messages
• Days 6–7: rest

Week 3

• Day 1: 18,000 messages
• Day 2: 25,000 messages
• Day 3: 35,000 messages
• Day 4: 50,000 messages
• Day 5: 70,000 messages

Week 4 onward

Double roughly every two days until you reach your target volume. By the end of week four, most senders can reach 200,000–500,000 messages per day on a single IP with a well-engaged list.

Who to Send to First

During warming, sequence your sends starting from the most engaged to the least engaged:

1. Recent openers and clickers (last 30 days)
2. Recent openers (last 90 days)
3. Customers and transactional contacts
4. Subscribers who opened in the last 6 months
5. Older subscribers and less-engaged segments — after warming is complete

The logic: high engagement during warming signals to mailbox providers that recipients want your mail. Early complaint spikes or low open rates during the warm-up period can stall or reverse your reputation gains.

Warning Signs During Warming

Watch these metrics daily when warming is active:

• Deferral rates above 5% — back off volume, give the IP another day before stepping up
• Spam complaint rate above 0.1% — stop warming to that mailbox provider domain; investigate your list
• Hard bounces above 2% — your list quality is too low; clean it before continuing
• Gmail Postmaster Tools showing "bad" reputation — reduce volume by 50% and hold for 3 days

Deferral messages like 421 Too many connections or 450 Try again later are normal early-stage warming signals. They're not failures—they're providers asking you to slow down, not stop. Retry deferred messages at reasonable intervals rather than abandoning them.

How Long Does Warming Take?

For senders with high-quality, engaged lists: 3–4 weeks to reach full production volume. For older lists or lower engagement: 6–8 weeks. For cold email scenarios where list engagement is inherently lower, a dedicated warming domain separate from your main domain is the right approach to avoid contaminating your primary sending reputation.

If you're setting up a dedicated IP through MailDog's SMTP relay, the documentation covers IP warming configuration specific to the platform. For the authentication prerequisites before you start, see the guide on common deliverability problems and fixes.