Warmbox vs Warmup Inbox (2026): Pricing, Features, and Which One to Pick

Warmbox and Warmup Inbox aren't the only two names that matter

Warmbox and Warmup Inbox dominate search traffic for email warmup, but they aren't the only credible options. The table below lines up five tools on starting price, ideal team size, and the one feature that sets each apart, so you can shortlist before reading the full breakdown.

2. Warmup Inbox

From $12/mo per inbox · Best for small teams under 4 inboxes · Granular per-inbox billing with no idle-seat waste

The tool uses the same warmup-pod mechanic as most of the category: real inboxes exchanging mail to build a sending history before you launch cold outreach. Billing is strictly per inbox, which per Warmup Inbox's pricing page keeps costs linear as you add mailboxes one at a time.

A 14-day free trial covers most of the initial ramp period, and the ESP integration list covers Gmail, Outlook, and most SMTP-based providers. Daily send volume per inbox caps lower than Warmbox's at the entry tier, which keeps new domains from ramping too aggressively.

Where it falls short: per-inbox billing turns expensive fast past ten mailboxes. An agency running 30 inboxes pays roughly three and a half times what Warmbox's flat tier charges for the same volume.

Do the math before you pick a side

Warmup Inbox is cheaper at three inboxes, and Warmbox is cheaper from four onward, so the right tool depends entirely on where your team sits today, not where it might be in a year. The table below runs the actual monthly cost at three team sizes using each tool's published pricing.

That gap compounds for agencies managing client domains at scale. A shop running 30 inboxes across five client accounts saves roughly $3,100 a year by picking Warmbox over Warmup Inbox, money better spent on domains and mailbox infrastructure than on a warmup meter that keeps climbing with every seat you add.

Team size decides this, not feature lists

Pick Warmup Inbox if you're under four inboxes and want to pay for exactly what you use. Pick Warmbox the moment you cross into double-digit mailboxes, since its flat tiers stop punishing you for scaling.

• Solo founder testing cold email with 2 to 3 inboxes: Warmup Inbox, lower absolute cost.
• Agency managing 15 or more client domains: Warmbox, flat tiers beat per-seat billing every time.
• Team already running Lemlist for outreach: look at Mailreach or Lemwarm instead, since neither Warmbox nor Warmup Inbox stitches into your sending tool natively.

If you're building cold email infrastructure from scratch, warmup is one piece of a bigger stack: domains, mailboxes, DNS records, and verified sending reputation all have to line up before warmup even matters. Modern Inbound's setup service handles that entire execution layer, including the 14-day warmup period, so you aren't stitching together five separate tools on your own.

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