Blog / Infrastructure

Shared vs Dedicated IPs for Cold Email Explained

20 May 2026

A shared IP sends your mail from an address used by many senders, so reputation is pooled and no warmup is needed; a dedicated IP is yours alone, giving full control of its reputation but requiring a slow warmup before it can carry real volume. For most cold-email senders the deciding factors are tenant isolation and domain health, not which IP type you pick — and managed Microsoft 365 setups sidestep the choice entirely.

What the two options actually mean

Every email leaves through a sending IP address, and mailbox providers attach part of their trust judgement to that IP. The shared-versus-dedicated question is simply whether that IP is used by one sender or many.

A shared IP is an address from a provider’s pool that carries mail from multiple customers at once. You inherit the pool’s combined reputation. There is nothing to warm up because the IP already has a sending history, but you also carry whatever the other senders on it do — good or bad.

A dedicated IP is reserved for you alone. Nobody else’s sending can drag its reputation down, and every signal it accumulates is yours. The cost is that a fresh dedicated IP starts from zero history, which mailbox providers treat with suspicion until you have proven the traffic is legitimate.

The tradeoffs side by side

Factor	Shared IP	Dedicated IP
Warmup needed	No — pool already has history	Yes — slow ramp from zero
Reputation control	Pooled with other senders	Fully yours
Risk from neighbours	Yes — bad senders can hurt you	None
Best fit	Lower or uneven volume	High, steady volume
Setup effort	Low	Higher (warmup + management)

The pattern is consistent: a shared IP trades control for convenience, and a dedicated IP trades convenience for control. Neither is universally better. The right answer follows your volume.

Why a dedicated IP needs warmup

A new dedicated IP has no track record, so providers cannot tell whether it belongs to a careful sender or a spammer. The way to resolve that is the same as warming a new domain: start with very low volume and raise it gradually so the IP earns a reputation through real, well-behaved sending.

This ramp typically takes from several days to a few weeks before the IP can carry campaign volume, similar to how long domain warmup takes. Push hard volume through a cold dedicated IP on day one and you teach providers to distrust it — the opposite of the point. A dedicated IP is only an asset once it has earned a reputation; until then it is a liability you have to manage.

There is also a volume floor. A dedicated IP needs enough steady traffic to maintain its reputation. Send too little and providers see an inconsistent, low-signal source, which can read as suspicious rather than trustworthy. Dedicated IPs reward senders who can keep them busy.

Where Microsoft 365 fits

Outbound mail from Microsoft 365 does not leave through an IP you own. It goes through Microsoft’s shared outbound pool, which Microsoft maintains and warms at the platform level. In the shared-versus-dedicated framing, a standard Microsoft 365 mailbox is effectively on a managed shared IP — but a very different kind of shared pool from a budget SMTP relay, because Microsoft actively polices it and removes abusive senders. (For the underlying difference between sending platforms, see Microsoft 365 vs Google Workspace for cold email.)

That changes the question. The isolation people actually want from a dedicated IP — my reputation is mine, not pooled with strangers — comes in this model from a different layer: a separate, isolated Microsoft 365 tenant and a separate sending domain for each domain you send from. Your domain reputation is fully yours even though the IP is shared, and you skip the fragile job of warming a raw IP from zero.

So which should you choose?

For most cold-email senders, the IP type rarely decides outcomes. Domain reputation, authentication (SPF, DKIM, DMARC), sending behaviour, and list quality matter far more than whether your IP is shared or dedicated.

A dedicated IP earns its keep when you send high, steady volume from a single brand and want absolute control of that IP’s history — and when you are willing to warm and maintain it. If you are spreading sending across multiple domains and mailboxes, as cold-email operators usually do, per-domain tenant isolation gives you the separation you wanted without the DIY warmup burden. Raw SMTP relays with cheap dedicated IPs are tempting on price, but raw SMTP is rarely a good base for cold email precisely because the reputation work lands entirely on you.

How Mailionaire approaches this

Mailionaire runs each sending domain in its own isolated Microsoft 365 tenant, so your reputation stays separated by domain without you ever warming a raw IP — warmup and authentication are handled, and worn mailboxes or domains get replaced as they wear out. US IP space is the default and usually better for US recipients; EU/Swiss residency is an optional add-on. Pricing is flat at $50 per active domain per month with no per-mailbox metering — see how it works.

FAQ

Is a shared or dedicated IP better for cold email?

It depends on volume. A dedicated IP gives you full control of its reputation but must be warmed up slowly before it can carry volume. A shared IP needs no warmup but mixes your sending reputation with other senders. For most cold-email senders, the IP choice matters less than tenant isolation and domain health.

Do I need to warm up a dedicated IP?

Yes. A brand-new dedicated IP has no sending history, so mailbox providers treat it with suspicion. You raise volume gradually over days to weeks so the IP earns a reputation. Skipping warmup on a fresh dedicated IP is one of the fastest ways to get mail filtered to spam.

Does Microsoft 365 give me a dedicated IP?

No. Outbound mail from Microsoft 365 leaves through Microsoft's shared outbound IP pool, which Microsoft maintains and warms at the platform level. You do not own or warm those IPs. Isolation in this model comes from a separate tenant and domain per sending domain, not from a dedicated IP.

Does the IP type make cold email legal?

No. Whether you have a shared or dedicated IP is a deliverability question, not a legal one. Permission to send depends on the recipient's jurisdiction — Germany's UWG §7(2) generally requires prior opt-in for advertising email, including B2B. The sender stays responsible. This is not legal advice.

---