EmptyInbox as a Mailinator Alternative
- Mailinator's free tier is public: anyone who guesses the address reads the mail
- Private inboxes and a private domain start at $79/month, billed yearly
- EmptyInbox inboxes are private to your API key at every tier, including the free one
- Mailinator still wins on load testing, SMS, team seats and long retention
The public inbox problem
Mailinator's free tier works because every inbox is public. There is no signup, which is genuinely useful, but the trade is that any address is readable by anyone who types it into the web interface. A verification link sitting in a public inbox is a verification link anyone can click.
For throwaway manual QA that is fine. For an automated flow creating real accounts on real services, it is a live credential leak. The usual fix is to move up to a paid plan with private inboxes and a private domain, which starts at $79 per month billed yearly.
EmptyInbox has no public tier to escape from. An address is only readable by the API key that created it, and that holds on the free tier as much as on a paid one. Addresses are randomly generated, so guessing one gets you nothing anyway.
| EmptyInbox | Mailinator | |
|---|---|---|
| Free tier privacy | Private, scoped to your API key | Public, readable by anyone |
| Free tier size | 5 inbox credits | Unlimited public inboxes |
| Cheapest private inboxes | $0, then $5 for 50 more | $79/mo, billed yearly |
| Pricing model | Prepaid credits, no expiry | Annual subscription |
| Payment | Bitcoin or USDT, no card, no KYC | Card or invoice |
| Signup required | Yes, or auto-register from the MCP server | No, for public inboxes |
| MCP server | Yes, npx emptyinbox-mcp |
No first-party MCP server |
| Private domains | No | Yes, on paid plans |
| SMS testing | No | Yes |
| Load testing | No | Yes, on higher plans |
| Retention | 7 days, then auto-deleted | Temporary on public, permanent storage on paid |
| Source | Open source | Proprietary |
Mailinator plan details checked September 9, 2026 against their public pricing page. Verify before budgeting.
What an agent flow looks like without a public inbox
Create the address, hand it to whatever is signing up, then wait. The wait is a blocking call rather than a polling loop you write yourself.
curl -X POST https://emptyinbox.me/api/inbox \
-H "Authorization: Bearer $EMPTYINBOX_API_KEY"
# swift.copper.owl@emptyinbox.meFrom an MCP agent, the same flow is three tool calls and no HTTP at all: create_inbox, then wait_for_message, then read the code out of the body. The address never appears anywhere a third party can read it.
- You want inboxes with no signup at all, and the mail is not sensitive
- You need addresses on your own domain
- You run email load tests at thousands of messages per second
- You need SMS testing or multiple team seats
- You need messages retained longer than 7 days
Frequently asked questions
Are EmptyInbox addresses public like Mailinator's?
No. Every inbox belongs to the API key that created it, and messages are only readable through that key. This is true on the free tier as well as paid.
Can I use EmptyInbox without signing up?
Not quite, but close. The MCP server auto-registers an account on first run, so there is no dashboard visit and no key to copy by hand. Over REST you call the register endpoint once and keep the key it returns.
How much does it cost to move off Mailinator's free tier?
On Mailinator, private inboxes start at $79 per month billed yearly. On EmptyInbox the first 5 inboxes are free and 50 more cost $5, with credits that never expire.
Does EmptyInbox support custom domains?
No. Every address is on emptyinbox.me. If your test depends on your own domain appearing in the address, Mailinator is the better fit.
What happens to messages after 7 days?
They are deleted automatically. There is no archive, no storage quota, and no cleanup job for you to run.