A retail client wanted to separate their transactional email onto a dedicated IP for better reputation isolation. They bought the IP on Monday and on Tuesday wanted to blast 500,000 emails through it.
Don't do this.
ISPs (Gmail, Outlook, Yahoo) track every sending IP they see. A new IP has zero history and zero reputation. Blasting high volume from it immediately makes the IP look like a spammer's throwaway server. Result: heavy filtering, spam folder placement, possible blocklisting.
The fix is IP warming - ramping volume gradually over weeks while ISPs learn the IP is a legitimate sender.
The 4-week ramp we use
Starting point is the engaged cohort - the 20% of subscribers who open consistently. These sends get high engagement signals, which is exactly what ISPs are using to judge the new IP.
| Week | Volume per day |
|---|---|
| Week 1 | 500 - 1,000 |
| Week 2 | 2,000 - 5,000 |
| Week 3 | 10,000 - 20,000 |
| Week 4 | 50,000+ |
By week 4 the IP has enough engagement history that full-list sends can run safely.
Rules during warming
Only send to engaged subscribers. The first 2-3 weeks are the most important moment in the IP's life - every bounce and complaint goes straight into the reputation model. Use the cleanest segment you have: subscribers who opened in the last 30 days.
Avoid low-engagement cohorts. Warming the IP with a list that hasn't been cleaned in 2 years is self-sabotage. High bounce rate on week 1 permanently damages the IP's starting position.
Monitor daily. Track bounce rate and complaint rate every day. If either spikes, pause the ramp and investigate before continuing.
Use Email Performance by Domain in Email Studio. Delivery rate varies by ISP - Gmail might be 98% while Yahoo is 70%. Per-domain visibility tells you which ISP is the problem.
When a dedicated IP is worth it
Dedicated IPs are not free and not always the right choice. Our rule:
- Under 250,000 emails/month: shared IP (cheaper, SFMC manages reputation across clients).
- 250,000 - 500,000/month: either, depends on complexity.
- Over 500,000/month, or high reputation sensitivity: dedicated IP.
Shared IP means the client's reputation is partially influenced by other SFMC customers sharing that IP pool. For most volumes that's fine. For high-volume or high-sensitivity senders, dedicated isolates the reputation.
Two mistakes we've seen
Blasting full volume on day one
IP gets blocklisted by Yahoo and Outlook in the first week. Takes 2-3 weeks to request delisting from each ISP and complete the warming from scratch. Every campaign scheduled in that window misses.
Cost of doing it right the first time: 4 weeks of ramp. Cost of doing it wrong: 4 weeks of ramp plus 2-3 weeks of delisting plus reputation damage.
Warming with an inactive list
Using a 2-year-old uncleaned list to warm a new IP. Bounce rate on week 1 is 8%. ISPs immediately flag the new IP as suspicious. The warming completes, but the IP carries below-average reputation permanently.
Always warm with the engaged, recently-active segment. If the engaged segment is small, the ramp starts smaller - that's fine. Don't pad volume with dormant subscribers.
Send Throttling helps during warming
Send Throttling (covered separately) limits per-hour send volume. Use it during warming to avoid dumping the daily allocation in the first 5 minutes. A smooth hourly rate looks more natural to ISPs than a burst.
Example: week 3 allocation of 20,000 emails, throttle to 2,000/hour. Send runs 10 hours. Looks like a legitimate large sender, not a blast.
When warming fails
If bounce or complaint rate spikes mid-warming:
- Stop the ramp at current volume. Don't escalate further.
- Investigate - was the data source bad? Was content off-brand?
- Fix the root cause.
- Resume at current volume for a few more days before continuing to ramp.
Do not repeat the original mistake of going fast. ISPs remember the first few weeks of an IP's life for months.
Takeaway
IP warming is a 4-week commitment that protects reputation for the life of the IP. Start with your most engaged subscribers, ramp volume gradually, monitor per-ISP delivery daily, and use Send Throttling to avoid bursts. The alternative - going fast and recovering from blocklists - is always slower and more expensive.
Standing up a new dedicated IP in SFMC? Our Salesforce team runs IP warming programs and deliverability optimization on production Marketing Cloud engagements. Get in touch ->
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