Blog / Pricing

Per-Mailbox vs Per-Domain Pricing for Cold Email

14 June 2026

Per-mailbox pricing charges a recurring fee for every inbox, so your bill grows with mailbox count. Per-domain pricing charges a flat fee per active sending domain no matter how many mailboxes it holds. Because cold email scales on mailbox count, the per-mailbox model climbs fastest and is the hardest to forecast, while per-domain pricing stays predictable as you grow.

This post compares the two billing models, shows how each behaves as you scale, and explains why the choice of unit — not the headline number — usually decides what you pay. The educational sections are vendor-neutral; we describe our own approach only at the end.

The two pricing models, defined

The billing unit is the thing a vendor multiplies to produce your invoice. In cold-email infrastructure, two units dominate.

Per-mailbox pricing charges a recurring amount for each individual mailbox. Common rates sit in the low single digits per mailbox per month. Sometimes there is an additional per-tenant or per-domain fee on top.

Per-domain pricing charges a fixed amount per active sending domain — the domain on the From address — regardless of how many mailboxes live on it. Mailbox count is not metered.

A sending domain is the domain you send from; a mailbox is one inbox on that domain. If you are new to these terms, the guide to how many mailboxes per domain covers the building blocks.

Why the unit matters more than the headline price

Cold-email infrastructure is not a buy-once setup. Sending domains wear out under sustained volume — often within a few months — so the standard practice is to run several overlapping domains, rotate across them, and replace worn ones. (We cover this in why cold-email domains burn out.)

That means usage trends upward over time. You add mailboxes. You add domains. A typical domain in this use case hosts on the order of 50 to 100 mailboxes, each sending a small, ramped daily volume.

The unit you are billed on decides how that growth hits your wallet. If your cost scales on the number that climbs fastest, your bill climbs with it.

How each model scales with growth

Here is the same growth path priced two ways. The per-domain side assumes a flat $50 per active domain (Mailionaire’s rate). The per-mailbox side uses an illustrative $3 per mailbox per month, near the middle of commonly advertised tiers — your real rate will differ, so treat the numbers as a model of behaviour, not a quote.

Setup	Mailboxes	Per-domain at $50/domain	Per-mailbox at ~$3/mailbox
2 domains	100	$100/mo	~$300/mo
5 domains	250	$250/mo	~$750/mo
10 domains	500	$500/mo	~$1,500/mo
20 domains	1,000	$1,000/mo	~$3,000/mo

The shape is the point. Both grow, but the per-mailbox line grows on the variable that rises fastest in cold email — mailbox count — while the per-domain line grows only when you deliberately add a domain. At high mailbox density, the gap widens at every step.

Density is exactly why this matters. If a vendor caps each domain at ~25 mailboxes, you need more domains (or more mailboxes) to reach the same volume. The model that holds up best is one where high density does not inflate the bill.

Forecastability: the deciding factor

The real difference is not which model is cheaper on a given day. It is which one you can predict.

To forecast a per-mailbox plan honestly, you have to forecast your future mailbox count — a number that depends on burn rate, rotation pace, and how aggressively you ramp. Most teams underestimate it, which is also a common driver of the year-two price shock.

To forecast a per-domain plan, you answer one operational question you already need an answer to: how many sending domains am I running? You size your domain count from your daily-volume targets and multiply by one flat figure. The fastest-climbing, least-predictable variable — mailbox count — drops out of the equation entirely.

Two properties make a flat per-domain model forecastable in practice:

1. The unit matches how you scale. You add domains as a deliberate planning decision, not by drifting past a mailbox allowance.
2. The renewal equals the signup. A flat price with no intro discount and no scheduled increase means month thirteen looks like month one.

None of this means per-domain pricing is always cheaper at every scale. It is a claim about predictability: a unit that matches your scaling and a renewal that equals your signup are the two things that prevent a budget surprise.

What to check before you compare quotes

The cold-email infrastructure market is crowded, and prices change. Per-domain/tenant pricing and per-mailbox tool pricing both vary by vendor and shift over time, and per-mailbox plans sometimes add a per-tenant fee on top. Always verify current pricing directly with the vendor before deciding.

When you compare, normalise the models against your own plan:

• Price the same target volume both ways. Pick a realistic mailbox count and compute the monthly total under each model, not the per-unit rate.
• Check the mailbox density cap. A low per-domain price with a 25-mailbox ceiling can cost more than a higher cap once you account for the extra domains you need.
• Ask what it renews at. An intro rate that resets quietly is the classic per-mailbox trap.
• Separate the sequencer from the infrastructure. Your sending tool is a different line item from the mailboxes and domains underneath it.

For a fuller breakdown of total cost, see our cold-email infrastructure cost guide.

How Mailionaire approaches this

We bill one way: a flat $50 per month per active sending domain, with up to 100 mailboxes on each domain and no per-mailbox meter, no minimum, and no year-two jump. Worn mailboxes and domains are monitored and replaced as they wear out, so density works for you rather than against your invoice. EU/Swiss residency is an optional add-on at roughly +20%; US IP space is the default. You can see the full model on our pricing page.

FAQ

What is the difference between per-mailbox and per-domain pricing?

Per-mailbox pricing charges a recurring fee for each individual inbox, so the bill grows with mailbox count. Per-domain pricing charges a fixed fee per active sending domain regardless of how many mailboxes sit on it. The two models behave very differently as you scale, because mailbox count climbs much faster than domain count.

Which pricing model is cheaper for cold email at scale?

It depends on mailbox density, but per-domain flat pricing is usually easier to forecast and often cheaper at high density. Cold email scales on mailbox count, so a per-mailbox meter grows exactly as you grow, while a per-domain price stays fixed even when each domain hosts many mailboxes.

Why does per-mailbox pricing climb fastest?

Cold email runs on volume, and volume comes from mailbox count. Going from 10 to 200 mailboxes is a 20x increase in metered units even if the per-unit price never changes. Because growth is built into the method, the per-mailbox meter rises every time you add capacity to hit your sending targets.

Does cheaper infrastructure make my cold email compliant?

No. Pricing model has nothing to do with legality. The recipient's jurisdiction governs, and rules like Germany's UWG §7(2) generally require prior opt-in for advertising email even B2B. Authentication and infrastructure help deliverability, not consent. You remain responsible for the legal basis of every send. This is not legal advice.

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