Infrastructure and sending practices: shared vs dedicated IP, warming, throttling

Behind every email program is the technical setup that determines how messages leave your ESP and reach inbox providers. While reputation and engagement carry the most weight in deliverability, your infrastructure choices still matter. The way you manage IPs, domains, and sending patterns can make or break your inbox placement.

Shared vs dedicated IPs
Most senders start on a shared IP, where many companies send from the same pool. Shared IPs work well for small to medium list sizes because the volume is spread across many senders, creating a steady baseline of activity. That stability makes inbox providers more comfortable, provided everyone on the pool follows good practices. The risk is that if one sender behaves poorly, it can drag down the entire pool.

Dedicated IPs are usually reserved for high volume senders who can sustain consistent activity on their own. If you are sending hundreds of thousands or millions of emails per month, a dedicated IP gives you control over your own reputation. The tradeoff is that you are fully responsible for keeping that reputation strong.

Best practices on shared IPs
Even on a shared IP, your behavior matters. If you send to unengaged subscribers, hit spam traps, or generate complaints, inbox providers will still associate those signals with your domain. Good hygiene and consistent sending protect both you and the rest of the pool.

IP and domain warming
When you start on a new IP or domain, inbox providers do not yet know if they can trust you. Warming is the process of gradually increasing volume so you build a track record of positive engagement. If you send too much too quickly, it looks suspicious and can cause blocks or spam placement. Warming requires patience, consistency, and a focus on your most engaged subscribers first.

A typical warmup plan might look something like this:

• Day 1: send 100 to your most engaged subscribers (people who have opened or clicked in the last 30 days).

• Day 3: increase to 500, again targeting your most active segment.

• Day 5: increase to 2000.

• Day 7: increase to 5000.

• Continue doubling every few days until you reach your normal sending volume.

The exact numbers depend on your list size, but the principle is the same: start small, send to engaged users, and ramp steadily.

How ESPs guide you
Most ESPs give you warmup instructions when you first get a dedicated IP or new sending domain. Some even automate throttling behind the scenes so you cannot send too much too quickly. Others provide a warmup schedule similar to the one above and ask you to segment your list accordingly. In all cases, the ESP is trying to protect your deliverability by pacing your sends until inbox providers trust your new setup.

What setup is right for you

• If you send fewer than 100,000 emails a month, a shared IP is almost always best. It gives you stability and avoids the risk of “cold” volume drops.

• If you send 100,000 to 500,000 emails a month, it depends on your engagement and consistency. Shared may still work, but you might consider a dedicated IP if your program is mature.

• If you send millions of emails per month, a dedicated IP is recommended so you own your reputation and can scale safely.

Key takeaway
Infrastructure and sending practices will not save you if your reputation is poor, but they create the conditions for a good reputation to grow. Whether you are on a shared or dedicated IP, the same rule applies: send consistently, warm carefully, and focus on engagement above all.

In the next article (article 7), we will look at monitoring and troubleshooting, and how to diagnose issues when deliverability starts to slip.

1. Intro to email deliverability

2. Authentication 101: SPF, DKIM, DMARC explained simply

3. How ISPs judge your emails: reputation, engagement, spam traps, complaints

4. List hygiene and data quality: why clean lists matter more than big lists

5. Content and design factors: subject lines, html, images, links, spam triggers

6. Infrastructure and sending practices: shared vs dedicated IP, warming, throttling

7. Monitoring and troubleshooting: how to use seed tests, blocklist checks, analytics

8. Future of deliverability: AI filters, gmail and yahoo changes, privacy trends