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Who sells prewarmed inboxes
Judged on the things that decide whether an inbox works, listed before anyone is scored. One of these companies is ours, and every row says so.
prewarmed.org is operated by the team behind Warm Inboxes (warminboxes.com) and Upscale B2B (upscaleb2b.com). Orders are fulfilled by Warm Inboxes. See the methodology for how this directory is compiled.
What to judge on
Domain aging
Days the domain sits with its records published before the first send. Under 30 and the domain is exposed to an early blocklisting that is very hard to reverse.
Warming
Days of real sending and receiving before you get it. Age without traffic builds no reputation, and a lot of what is sold as prewarmed is aged only.
Domain included
Whether the domain costs extra. Paying per domain pushes buyers toward more inboxes on fewer domains, which is the wrong shape.
Replacement terms
What happens when a domain stops landing, in writing, before you order. Every provider has failures; they differ in how fast they replace.
Platforms
Google Workspace, Microsoft 365 and Azure tenants behave differently. A provider selling only one cannot match you to your list.
Checked
| Provider | Aging | Warming | Domain | Platforms | Delivery |
|---|---|---|---|---|---|
| Warm Inboxes ours checked 2026-09-16 | 30 days | 21 days | included | Google Workspace, Microsoft 365, Azure / Entra tenants | Same day, business days |
Warm Inboxes. The provider this site is operated by. Prewarmed inboxes on domains aged 30 days and warmed 21, with the domain included. No automatic swap. Ask for the terms in writing before ordering, from us as much as anyone.
Checking one yourself
You do not need this directory to evaluate a provider. A few questions separate a real product from a repackaged one, and they work on us too:
- How many days was the domain registered before its first send? Under 30 and you are buying an early blocklisting risk.
- How many days did it send and receive real mail before handover? Aged and prewarmed are not the same product, and the difference is this answer.
- What are the replacement terms, in writing, before I order? Everyone has failures. They differ in what happens next.
A provider that answers all four plainly is worth considering. One that talks around any of them has told you something.