Every message you send leaves from an IP address, and mailbox providers keep a reputation score for that IP alongside the one they keep for your domain. The question is whether that IP is yours alone or shared with other senders — and the right answer depends almost entirely on how much mail you send and how consistently you send it.
How each model works
On a shared IP, your ESP routes your mail through a pool of addresses used by many customers at once. The IP’s reputation is the aggregate of everyone’s behaviour on it. Good ESPs curate these pools carefully — verifying senders, enforcing complaint limits, and removing bad actors — so the pool stays warm and reputable through sheer collective volume. You inherit that established reputation from day one, with no warm-up of your own.
On a dedicated IP, every message goes out from an address only you use. Its reputation reflects your sending and nobody else’s. That’s powerful control, but it comes with responsibility: you have to warm the IP up from zero, and you have to keep it warm with steady volume forever after.
The core trade-off: control vs volume
A dedicated IP’s appeal is isolation. Your reputation is entirely your own — no other sender’s spam complaints or trap hits can drag you down, and your good behaviour isn’t diluted by anyone else’s. For a large, disciplined sender, that control is worth a lot.
But that same isolation is the catch. IP reputation is a moving average of recent activity, and providers need to see enough consistent volume from an IP to form and hold a stable opinion of it. A dedicated IP that sends too little never accumulates enough recent signal — its reputation stays “unknown” or swings wildly with every send. As a widely-used rule of thumb, a dedicated IP needs on the order of tens of thousands of messages per week, sent regularly, to stay reliably warm. Below that threshold, a dedicated IP is usually worse than a shared one, because you get all the fragility of owning a reputation with none of the volume needed to stabilise it.
Why low-volume senders should stay shared
If you send occasionally, in spiky bursts, or below roughly tens of thousands per week, a shared IP is almost always the better choice. On a shared pool, other reputable senders’ steady volume keeps the IP warm for you, so your intermittent sends still leave from a trusted address. Put that same intermittent volume on a dedicated IP and there isn’t enough activity to build reputation — every campaign effectively re-warms a cold IP, and deliverability suffers. Low-volume senders get better inbox placement, and far less operational hassle, by staying shared and focusing their effort on domain reputation, which they control regardless of IP.
When a dedicated IP makes sense
- High, consistent volume. You reliably send enough mail every week to keep the IP warm. This is the single most important prerequisite.
- You want full control of IP reputation. You’d rather own your reputation outright than share a pool’s fate — and you have the volume to back that up.
- Sensitive or high-stakes mail. Transactional streams (receipts, password resets) where you can’t afford another sender’s behaviour affecting delivery. Often paired with separating streams onto their own subdomains.
- Predictable, disciplined sending. You maintain clean lists, low complaints and a steady cadence, so a dedicated IP’s reputation stays strong rather than decaying between sends.
If you do move to a dedicated IP, it starts at zero reputation and must be warmed up carefully — follow how to warm up a dedicated IP.
What matters regardless of which you pick
The IP model is only one input into deliverability, and for most senders not the most important one. Domain reputation travels with you across any IP, so aligned SPF, DKIM and DMARC, clean lists and low complaints matter on shared and dedicated alike. Whichever you choose:
- Publish and align authentication, and verify it with the Email Health Check and DMARC Checker.
- Confirm reverse DNS with the Reverse DNS Checker — a dedicated IP in particular needs a clean, matching PTR.
- Keep lists clean with the Email Verifier and watch your bounce rate.
- Check blocklist status periodically with the Email Blacklist Check.
The bottom line
Choose based on volume first. If you send a high, consistent stream of mail and want to own your reputation outright, a dedicated IP — properly warmed and maintained — gives you the most control. If you send less than that, or in unpredictable bursts, stay on a reputable shared pool and put your effort into domain reputation and list quality, which decide inbox placement no matter which IP your mail leaves from.
Sources
IP reputation is scored per-provider and reported directly by receivers such as Google Postmaster Tools and Microsoft SNDS. Volume thresholds for keeping a dedicated IP warm are industry rules of thumb rather than published figures, and vary by ESP and receiver. The authentication that makes domain reputation portable across IPs is defined in RFC 7489.