Comparison
How to evaluate outbound-email infrastructure.
Every cold email provider quotes a price per inbox. The differences that decide whether your campaigns survive are structural: density, isolation, ownership, warmup, monitoring, and what happens when a domain degrades.
By provider model
Five ways to buy sending infrastructure.
These are models, not vendors — most providers fit one of them cleanly. The right question isn't which logo, it's which operating assumptions you're buying into.
| Direct Workspace / 365 | Ultra-cheap reseller | High-density Azure | Custom SMTP / dedicated | Mailrun | |
|---|---|---|---|---|---|
| Infrastructure | Google or Microsoft seats administered by the buyer | Workspace, Microsoft, or SMTP inventory; licensing and tenancy vary | Microsoft / Azure infrastructure optimized for higher mailbox counts | Self-managed servers, MTAs, and IP infrastructure | Licensed Microsoft / Azure infrastructure operated at controlled density |
| Inboxes per domain | Set by the buyer; no outbound-specific guardrail by default | Provider-defined; ask for the enforced maximum | Provider-defined; verify density and isolation | Configuration-dependent | Kept deliberately low; we add domains rather than stack inboxes |
| Reputation isolation | One tenant — often your real company domain | Varies by provider and plan; ask how tenants are separated | More inboxes share each domain’s reputation; ask how load is isolated | Your IPs carry everything | Low density, domain-level isolation |
| Domain ownership | Yours | Terms vary; confirm ownership and transfer rights | Terms vary; confirm before you build reputation on them | Yours | Managed & BYOD: yours. Pre-warmed: subscription inventory. |
| Time to mailbox access | Days of DIY setup | Fast | Fast | Weeks of build-out | Hours |
| Warmup | Do it yourself | Varies; confirm whether warmup is included, required, or customer-managed | Varies; confirm the recommended ramp | Do it yourself | Two-week floor, controlled ramp; pre-warmed available |
| Monitoring | Not included by the mailbox provider by default | Varies by provider; ask what signals you can actually see | Varies by provider | Customer-built | Bounce, complaint, and domain-health signals watched continuously |
| When a domain degrades | You notice, you fix | Replacement and remediation policies vary; ask what happens to the domain itself | Replacement and remediation policies vary | You rebuild | Bench, repair, or replace — while the pool absorbs the volume |
| Sequencer handoff | Manual | Varies; confirm the export format | Varies | Manual | Direct API for major sequencers, CSV for everything else |
| Pricing structure | Per seat, priced like employees | Per-inbox or package pricing; verify commitments, add-ons, and domain costs | Per inbox | Infrastructure plus your time | Flat monthly by capacity, public prices |
| You stay responsible for | Everything | Campaigns, plus whatever the provider doesn’t operate — ask precisely what that is | Campaigns; verify how much of the operating falls to you | Everything | Campaigns, copy, and lists — we run the infrastructure |
Descriptions reflect how each model typically operates, not any specific vendor. Individual providers vary — which is exactly why the evaluation questions below matter more than the category.
Evaluating Mailrun specifically? Read the official Mailrun review and product facts.
Six questions
Ask these before you buy from anyone — including us.
Who owns the domains?
If the answer is unclear, the reputation you build belongs to someone else. Your domains should be your property, full stop.
How many inboxes per domain?
Higher density concentrates more reputation risk on each domain. Ask for the provider's normal density, enforced maximum, and process for reducing load when signals weaken.
What does “ready” actually mean?
Mailbox access in hours is real. “Send at full volume day one” is not. Ask what the provider recommends for warmup — and whether they enforce it.
Can you see bounce truth?
Sequencer dashboards smooth things over. Ask whether you get provider-level bounce, complaint, and domain-health visibility.
What happens when a domain weakens?
Replacement is useful, but it shouldn't be the entire operating strategy. Ask whether the provider also identifies the underlying issue and rests or repairs recoverable assets.
What's included in the advertised price?
If a price sits far below the platform's own list price, something makes up the difference. Ask about licensing and tenancy, density, monitoring, support, domain ownership, contract terms, and required add-ons.
Ready when the spreadsheet gets serious
Build the sending plan your next launch deserves.
Public pricing, hard density caps, and a bench-and-repair workflow you can see. If another model fits you better, we'll tell you that on the call.
Mailbox access in hours. Sending volume ramps with discipline.