What is a phased migration strategy for moving to a new IP/domain?

Switching to a new IP or domain is one of those things where going too fast can genuinely wreck your sender reputation. Mailbox providers like Gmail and Outlook have no history with your new infrastructure, so they're watching closely. The whole point of a phased migration is to build that trust incrementally instead of dumping your full list on day one and hoping for the best.

Here's how a solid phased migration actually works, with real numbers and checkpoints.

Phase 1: Set up properly before a single email leaves

Get your SPF, DKIM, and DMARC records configured on the new domain before anything else. Send a handful of test messages to your own inboxes (Gmail, Outlook, Yahoo) and check the headers to confirm authentication is passing. If auth isn't clean at this stage, stop. Don't move forward until it is. (This sounds obvious, but it's the most common skip.)

Phase 2: Warm up with your most engaged subscribers

Start routing only a small slice of volume through the new infrastructure. A reasonable starting point is 5 to 10 percent of your total list, and it should be your most engaged segment. These are people who've opened or clicked in the last 30 to 60 days. They're the readers most likely to engage positively, which is exactly the signal you need mailbox providers to see early on.

Keep the rest of your traffic on the old infrastructure for now. Run both in parallel and monitor both sets of metrics daily. You're watching for bounce rates above 2 percent, spam complaint rates above 0.1 percent, and any inbox placement shifts. If numbers look clean after 7 to 10 days, you're ready to expand.

Phase 3: Ramp volume gradually

This is the actual warm-up schedule. A typical ramp might look like this over four to six weeks:

• Week 1: 5 to 10% on new infrastructure
• Week 2: 20 to 25%
• Week 3: 40 to 50%
• Week 4: 70 to 80%
• Week 5 or 6: 100%

Slower is better if your list is large or your current reputation has any soft spots. Faster ramps are riskier because any complaint spike at high volume will hurt more than the same spike at low volume. As volume shifts to the new infrastructure, be just as watchful. Don't stop monitoring the old one either until it's fully deprecated.

Phase 4: Full cutover and deprecation

Now once 100% of your traffic is running cleanly on the new infrastructure for at least a week with stable metrics, you can retire the old setup. Don't rush the deprecation. Keep the old domain and IP configured for a little longer in case you need to roll back. Having that option is worth the small overhead.

After full cutover, keep watching your reputation recovery signals for at least another 30 days. Bounce rates, complaint rates, and inbox placement are your three core KPIs throughout the entire process.

If anything looks off at any phase, pause and diagnose before moving forward. A phased migration only works if you actually treat each phase as a checkpoint, not just a calendar entry. If you want a second set of eyes on your setup before you start, our SOS hotline is free and we're happy to walk through it with you.