Quick answer
Mailinator - Mailinator wins for most builders because its free tier covers a broader, more practical testing workflow with no sign-up required, while AgentMail is better only if you specifically need a programmable inbox API for agents.
How the free tiers compare
These two free tiers solve different problems, even though both touch email. AgentMail is an inbox API for AI agents and automation, so its free plan is about a small amount of real capacity: 3 inboxes, 3,000 emails per month, 3 GB storage, a couple of webhook endpoints, and 2 team members. Mailinator is a workflow testing tool for QA and developers, and its free plan is much broader in practice: unlimited public inboxes, temporary storage, no sign-up required, SMS testing, API access, webhooks, routing rules, load testing, and message attachment support. That means AgentMail is narrower but more oriented around building against inbox objects and agent workflows, while Mailinator is better when you need to validate sign-ups, OTPs, password resets, and similar message-driven flows. Both free tiers are permanent and do not require a credit card.
AgentMail vs Mailinator free tier, side by side
| AgentMailFTV 47 | MailinatorFTV 74 | |
|---|---|---|
| Free inboxesAgentMail limits real inbox count; Mailinator’s free plan is public and unlimited. | 3 inboxes | Unlimited public inboxes |
| Email volumeMailinator’s free tier description does not give a monthly email quota. | 3,000 emails/month | Unlimited public inbox usage; no explicit monthly email cap listed on the free plan |
| StorageAgentMail gives fixed storage; Mailinator’s free plan is temporary-only. | 3 GB | Temporary storage |
| WebhooksMailinator includes webhooks without a stated endpoint count. | 2 webhook endpoints | Webhooks included |
| Team membersMailinator’s free plan details here do not list seat limits. | 2 team members | Not specified on the free plan |
| Credit card requiredBoth inputs explicitly say no credit card is required. | No | No |
After you outgrow the free tier
AgentMail’s first paid tier is Developer at $20/month, with flat pricing and clear quota jumps to 10 inboxes, 10,000 emails per month, 10 GB storage, and 10 custom domains. Mailinator’s first meaningful paid tier is Business at $79 per month billed yearly, also flat-priced, but aimed at private inboxes, private domains, more storage, higher throughput, and 5 seats. For small teams, AgentMail is much cheaper if you just need more controlled inbox capacity. Mailinator costs more, but its paid plans move you into private testing infrastructure rather than simply scaling inbox count.
Cost at real usage
| Usage | AgentMail | Mailinator |
|---|---|---|
| 1 small prototype team needing paid capacityClosest first paid tier comparison; Mailinator’s Business plan is billed yearly. | $20/mo | $79/mo |
| 10 inboxes and up to 10,000 emails/monthAgentMail’s Developer tier matches this scale; Mailinator requires Business for private inboxes. | $20/mo | $79/mo |
| 5 seats with private testing workflowsMailinator Business includes 5 seats; AgentMail’s provided plans do not list comparable seat-based team scaling. | No matching paid tier in provided data | $79/mo |
| 150 inboxes and 150,000 emails/monthAgentMail’s Startup tier matches this scale; Mailinator’s next provided tier is far above this and is priced from $159/mo billed yearly for 300K emails/month. | $200/mo | No matching paid tier in provided data |
Estimates, not quotes. Usage-based rates change - verify with the vendor's pricing page before committing.
When to pick each one
Pick AgentMail when…
- You are building an AI agent that needs programmatic inbox creation and message handling.
- You need a small number of real inboxes for a prototype, internal tool, or demo.
- You care about custom domains and structured email data extraction later on.
- You want a free plan with explicit inbox, email, storage, and team quotas for a controlled pilot.
Pick Mailinator when…
- You are testing sign-up, OTP, password reset, or other message-driven flows.
- You want unlimited public inboxes for QA without creating accounts.
- You need SMS testing alongside email in the same free workflow.
- You want API access, webhooks, routing rules, and load testing on the free plan.
- You do not want to sign up before trying the product.
Bottom line
For the most common builder looking at a free tier, Mailinator is the better pick because it lets you test real message flows immediately, with unlimited public inboxes and useful QA features at no cost. AgentMail is the better choice only when the inbox itself is the product surface you are building against, especially for AI-agent automation. If you expect to outgrow the free tier, AgentMail also has a much cheaper first paid step, while Mailinator’s paid plans are more expensive but cover a broader private-testing setup.
Read the full listings: AgentMail and Mailinator. Scores use the FTV methodology at /ftv. Browse more head-to-heads on /compare, or see the top-ranked free tiers on /top.