First-party sources checked 2026-07-15

Coldrig vs AgentMail: cold-outreach platform vs. raw inbox API

This is not really a fair fight, and we'd rather say so than fake a rout. Use AgentMail when an agent needs its own raw, programmable inbox — send, receive, reply, search, threaded email over MCP — and you're prepared to build sequencing, warmup, and suppression yourself. Use Coldrig when you want the cold-outreach lifecycle — domains, mailboxes, warmup, campaigns, replies, suppression — as one managed layer your agent drives with a single token. AgentMail is the inbox-primitive layer; Coldrig is a full lifecycle built on top of that kind of primitive. Comparing sticker price alone would be slop.

Why compare against a different category? AgentMail is the best-funded, best-documented "MCP inbox for AI agents" result a discovery query returns, and it's frequently the first thing a research pass finds when searching for agent-operated email. A real buyer-agent research run we conducted independently evaluated AgentMail directly and rejected it for exactly this reason: "It is explicitly not built or marketed for cold email / warmed mailbox fleets; it's an agent-native inbox API for transactional/conversational use — category mismatch." (Our own internal buyer-agent research run, blind shopper, 2026-07 — not a marketing claim about AgentMail.)
No fabricated numbers Every AgentMail figure below is sourced from agentmail.to's own pricing page and public site, fetched directly 2026-07-15. Coldrig figures come from the current pricing page. No deliverability, open-rate, or reply-rate comparison is made anywhere on this page.

Fast decision table

RequirementAgentMailColdrig
Raw programmable inbox over MCPYes — this is the entire productYes, as one part of the lifecycle
Cold-outreach lifecycle (domains → mailboxes → warmup → campaigns → replies)No — confirmed no campaign, sequence, or cold-outreach layer anywhere in AgentMail's own marketingYes, one managed lifecycle behind setup_infrastructure and launch_campaign
Warmup / deliverability toolingNone found beyond standard SPF/DKIM/DMARC authBuilt-in warmup state, tracked per mailbox
Suppression / unsubscribe complianceNone found — consistent with not being built for outbound marketing mailServer-enforced suppression and unsubscribe by default
MCP discovery-file hygieneBest of any cold-email-adjacent vendor researched — its own /.well-known/mcp/server-card.json resolves liveAlso live — see our server card
Funding / credibility signal$6M seed led by General Catalyst (announced March 2026), YC S25 — best-credentialed vendor in this comparison setEarly access, self-funded, no external round to disclose
Entry price at 10 inboxes/mailboxesDeveloper tier: $20/mo, 10 inboxes, no cold-outreach tooling included$149/mo, 10 provisioned mailboxes, full lifecycle included
Live production track recordYes — a shipped, paying-customer productNo — Coldrig is early access; the API, MCP endpoint, and sandbox are live, but real sending is not active yet (see FAQ)

Where AgentMail is honestly stronger

Why this isn't the head-to-head it looks like

AgentMail's own site describes exactly what it is: "Email for AI Agents — give an agent its own inbox to send, receive, reply, search, and manage threaded email over MCP," explicitly distinguished from transactional ESPs like SendGrid. There's no mention anywhere in their marketing of campaign management, sequence automation, or cold outreach. If your agent needs to run actual cold outreach — multiple mailboxes working in concert, staged warmup ramps, per-mailbox send caps, unsubscribe/suppression enforcement, campaign-level reply handling — AgentMail gives you the inbox and leaves the rest to you. That's the same DIY cost calculus covered in our DIY comparison, just starting one layer higher: the inbox is provisioned, but the sequencing, warmup, and compliance logic is still your job, and still has to be re-derived by your agent every session.

Pricing: compare what you're actually buying

AgentMailColdrig
Free tier$0/mo — 3 inboxes, 3,000 emails/mo, 100 emails/day cap, 3 GB storageFree sandbox — full simulated pipeline, no real domains, mailboxes, or spend
Entry paid tierDeveloper: $20/mo — 10 inboxes, 10,000 emails/mo (no daily cap), 10 custom domains, email support. No sequencing, no warmup, no unsubscribe handling at any tier.$99/mo for 5 provisioned mailboxes, then $10/mo per additional mailbox (a $49 platform fee plus $10/mailbox, five-mailbox minimum): $149 for 10, $249 for 20, $649 for 60.
Send quota / billing meterFree tier caps at 100 emails/day; Developer and Startup tiers publish a monthly email count (10,000 / 150,000) but these describe raw inbox API throughput, not a cold-campaign sending program.No send quota — sends are not the billing meter. Planning capacity ≈3,300/mo at 5 mailboxes (same physics on any platform; non-contractual planning guidance, not a purchased allowance — see the calculator).
Mid tierStartup: $200/mo — 150 inboxes, 150,000 emails/mo, SOC 2, Slack support. No tier between $20 and $200 (no ~30-50 inbox option).$249/mo at 20 mailboxes, $649/mo at 60 — a continuous curve, no pricing cliffs.

AgentMail's Developer tier is real money saved if a bare inbox is genuinely the whole requirement. It stops being a fair price comparison the moment cold-outreach features enter the requirement, because AgentMail doesn't sell any — the entire sequencing, warmup, and compliance layer would need to be built and held in your agent's own state, which is exactly the friction the DIY comparison quantifies.

Bottom line

If the requirement is "give my agent a raw, well-documented inbox and I'll build the rest," AgentMail is a strong, credible, better-funded choice, and its MCP discovery hygiene is worth learning from. If the requirement is "run cold outreach — sequences, warmup, replies, suppression — without re-deriving that state every session," Coldrig is built for exactly that and AgentMail isn't built for it at all. Re-run this comparison if AgentMail ships a cold-outreach layer; nothing in their public roadmap suggests that today.

Related

Sources and verification