How to Warm Up a New IP or Sending Domain

Start sending at full volume from a brand-new IP and your mail will likely hit the spam folder — or get blocked entirely. The fix is IP warming: gradually increasing your sending volume so mailbox providers learn to trust you. The same logic applies to a new sending domain. This guide explains why warming matters, gives you a practical ramp-up approach, and shows what to watch along the way. Warm up properly and you build a reputation that pays off for years.

Why warming up is necessary

Mailbox providers like Gmail, Outlook, and Yahoo decide whether to trust you based on sender reputation — a track record built over time. A new IP or domain has no track record at all. From the provider’s perspective, a fresh sender suddenly blasting thousands of emails looks exactly like a spammer or a hijacked server.

Warming up solves this by sending in steadily increasing batches. Each batch that gets opened and avoids complaints tells providers “this is a legitimate sender people want to hear from.” Skip the warm-up and you risk:

• Mail landing in spam from day one.
• Throttling, where providers deliberately slow your delivery.
• Outright blocks or even a blacklisting.

IP warming vs domain warming

Two related but distinct things build reputation:

• IP reputation is tied to the sending IP address. It matters most on dedicated IPs, where the reputation is entirely yours.
• Domain reputation is tied to your sending domain and follows you even if you change IPs.

If you’re on a shared IP through an email platform, the IP reputation is largely managed by the provider and shared across many senders — you mostly focus on domain reputation and good sending habits. If you have a dedicated IP, you must warm both. Either way, warming the domain by ramping volume gradually is always worthwhile.

Before you start

• Authentication is in place. SPF, DKIM, and DMARC must all be set up and passing — see the email authentication guide. Warming an unauthenticated sender wastes the effort.
• Your list is clean and engaged. Warm up using your best contacts — people who recently signed up and reliably open. Never warm up on an old or purchased list.
• You can segment by engagement. You’ll send to your most active contacts first.
• You have a baseline plan for volume. Know roughly how many emails you ultimately need to send per day.

The warming principle: start small, grow steadily

There’s no single universal schedule — the right pace depends on your total volume, your provider, and how engaged your list is. But the principle is always the same: begin with a small batch and increase gradually over several weeks, watching your metrics at each step.

A typical approach looks like this:

1. Day 1: Send to a small batch of your most engaged contacts.
2. Following days: Increase the volume incrementally each day or every few days.
3. Continue ramping until you reach your target daily volume.
4. Hold steady once warmed — sudden spikes can undo your progress.

If you’re sending modest volumes, warming may take a couple of weeks. Large senders ramping to high daily volumes should expect to take longer and increase more cautiously. The bigger your target volume, the more gradual the climb should be.

Step-by-step warm-up process

Step 1: Segment your best contacts

Sort your list by engagement and start with the people most likely to open and click. Positive engagement early on is the single biggest reputation booster. Save your less-engaged contacts for later in the warm-up, or sunset them entirely.

Step 2: Send valuable, expected mail

Warm up with content people actually want — a welcome series, a useful newsletter, or a genuine offer. Don’t warm up with a risky promotion or a re-engagement blast to dormant contacts. The goal is opens and replies, not just sends.

Step 3: Ramp volume gradually

Increase your daily send according to your plan. Resist the temptation to jump ahead, even if early numbers look great. Consistency beats speed.

Step 4: Spread sends across providers

Your list probably mixes Gmail, Outlook, Yahoo, and others. Each builds reputation independently, so warming across all of them as you ramp is healthy. Most email platforms handle this automatically when you send to a normal list.

Step 5: Monitor and adjust

After each step, check your metrics (below). If complaints rise or inbox placement drops, slow down — hold at the current volume or step back — until things stabilize. Warming is responsive, not rigid.

What to monitor while warming

• Delivery and bounce rates. Rising bounces mean list problems — clean them up. (See hard bounce vs soft bounce.)
• Open and click rates. Strong engagement is the signal you’re trying to generate.
• Spam complaint rate. Any meaningful rise is a red flag — slow down immediately.
• Inbox placement. Use seed tests across major providers to confirm you’re landing in the inbox, not just being “delivered.”
• Provider feedback. Some providers offer postmaster tools that show your reputation directly.

Common warm-up mistakes

• Ramping too fast. The most common error. Patience is the whole point.
• Warming on a bad list. Old or purchased contacts generate bounces and complaints that defeat the exercise.
• Inconsistent sending. Big gaps or erratic volume confuse providers. Send regularly.
• Ignoring the metrics. Warming is a feedback loop; if you don’t watch the numbers, you can’t adjust.
• Skipping authentication. No SPF/DKIM/DMARC means no foundation to build reputation on.

FAQ

How long does IP warming take? It depends on your target volume and list engagement. Smaller senders may warm up in a couple of weeks; large senders ramping to high daily volumes should plan for longer and increase more slowly.

Do I need to warm up on a shared IP? The shared IP’s reputation is largely managed by your provider, so the IP-warming burden is lighter. You still benefit from ramping volume gradually to build your domain reputation and good sending habits.

Can I speed up the process? Not safely. Pushing volume faster than providers will trust risks spam folder placement, throttling, or blocks — which sets you back further than going slow would have. Send to your most engaged contacts to build trust as efficiently as possible.

What if my metrics drop mid-warm-up? Slow down. Hold at your current volume or step back until complaints fall and placement recovers, then resume ramping more cautiously.

Bottom line

IP warming is about earning trust the honest way: start small, send mail people want, ramp gradually, and watch your metrics. Pair it with solid authentication and a clean list and you’ll build a durable sender reputation — giving Vaillant a clear path to the inbox. For the full picture, see our email deliverability guide.