IP warming from zero without wrecking deliverability

Moving to a new email platform means moving to new sending infrastructure, and mailbox providers have no history with your new IP addresses. They treat an unknown sender cautiously, which is reasonable of them and inconvenient for you.

The fix is warming: a deliberate ramp in volume over two to four weeks, sending to your most engaged contacts first, so providers build a positive record before you send anything at scale. Rush it and you land in spam folders that take months to climb out of.

We have run this process on migrations of several million profiles. The plan below is the one we use, and the order of the steps matters more than the exact daily numbers.

Fix authentication before you send a single message

Warming an IP with broken authentication teaches providers that your mail is suspicious. Everything in this section must be verified before day one of the ramp.

• SPF record published for the sending domain, with the new platform's infrastructure included and the record under the ten lookup limit.
• DKIM signing enabled with a 2048-bit key, and the signing domain aligned with the visible From domain.
• DMARC published, starting at p=none with an aggregate reporting address someone actually reads.
• A dedicated sending subdomain for marketing traffic, kept separate from transactional and corporate mail.
• Reverse DNS on each new IP resolving to a hostname on your own domain.
• Feedback loops registered with the providers that offer them, routed into your suppression logic automatically.

Send a seed test to a spread of Gmail, Outlook, Yahoo and corporate addresses. Check headers, not just the inbox placement, and confirm that both SPF and DKIM pass with alignment.

Build the seed list from proven engagement

The warming audience is the most important decision in the whole exercise. You want contacts who reliably open, click and reply, because positive engagement signals are what build the reputation.

Define the seed list as people who have opened or clicked in the last thirty days, have a valid purchase or login in the last ninety, and have never complained or hard bounced. In most programmes that is between five and fifteen per cent of the file.

Sort that group by recency of engagement and mail it in descending order. Your best contacts see the first send, your merely good contacts join in week three. If your audit surfaced a data quality problem, resolve it before building this list, since the CRM audit checklist exists precisely to catch that kind of issue early.

Ramp the volume across four weeks

A common shape doubles daily volume each day for the first week, then continues doubling every second day, holding steady whenever metrics wobble. Something like this works for a file of a few hundred thousand:

• Days one to three: 200, 500, 1,000 per IP, sent to the most engaged decile only.
• Days four to seven: 2,000, 5,000, 10,000, 20,000, still inside the top engagement tier.
• Week two: 40,000 to 100,000 per day, adding the next engagement tier once complaint rates stay flat.
• Week three: 150,000 to 400,000 per day, introducing your regular campaign content rather than warming sends.
• Week four: full volume, with the least engaged segments reintroduced last, or not at all.

Send at a consistent time each day. Providers read volume spikes as a signal, and an erratic schedule during warming looks like exactly the thing they filter.

Hold the ramp, do not reverse it, if a metric breaks threshold. Reversing volume sharply is itself a signal worth avoiding.

Watch the signals that decide the outcome

Blended metrics will not tell you what is happening. Break every number down by mailbox provider, because Gmail and Microsoft respond to different things and usually fail at different points in the ramp.

Thresholds we hold to during warming:

• Complaint rate under 0.1 per cent per provider. Above 0.3 per cent, pause and cut the audience back to the previous tier.
• Hard bounce rate under 2 per cent. A spike here means the list is older than someone told you.
• Open rate materially above your historical average, because a warming list should outperform your file.
• Deferrals and throttling messages read daily from the platform logs, not weekly.

Deferrals are normal early on. Persistent 4xx responses from one provider after week two mean that provider is not convinced, and the answer is usually tighter audience selection rather than more volume.

On our Premier Padel work, careful warming took delivery past 99 per cent and supported open rates above 45 per cent once the programme reached full volume. That outcome came from patience during the ramp, not from anything clever afterwards.

Plan the hand-off to business as usual

Warming does not end when you hit full volume. Reputation decays with silence, so a dedicated IP needs a reasonably consistent weekly cadence to stay healthy.

Keep the suppression rules you built during warming. The inactivity window, the complaint routing and the bounce handling were doing real work, and quietly dropping them a month later undoes the ramp.

Document the whole exercise: dates, volumes, audiences and provider metrics. The next migration, or the next new IP, starts from evidence instead of memory. This is the same discipline we apply across our implementation projects.

What to do this week

• Verify SPF, DKIM, DMARC and reverse DNS on the new sending domain, and send a seed test that confirms alignment in the headers.
• Build and export the warming seed list, sorted by engagement recency, and check what share of your file it represents.
• Draft the daily volume schedule with named audience tiers, and agree the complaint and bounce thresholds that will pause the ramp.