Mail Blackhole Comparison
Free email sandbox plans compared — Mailtrap, Mailisk, Mailloop and MailSlurp vs our Mail Blackhole fake SMTP mailboxes: monthly quotas, retention, API, IMAP and webhooks.
All five services have a free tier — the differences are in the limits. Ours swaps a monthly send quota for storage-based caps, so the number of emails you can capture is not reset by a billing cycle.
| Mail Blackhole | Mailtrap | Mailisk | Mailloop | MailSlurp | |
|---|---|---|---|---|---|
| Free quotas | |||||
| Emails per month | No monthly cap | 50 | 500 | 500 | 500 inbound |
| Inboxes | 10 mailboxes | 1 sandbox | 1 namespace | 1 sandbox | 50 inboxes |
| Messages kept per inbox | 100 + 50 MB (FIFO) | 10 (FIFO) | until expiry | 200 | 200 MB total |
| Retention | 30 days, pinned exempt | until evicted | 1 day | until evicted | until deleted |
| Max message size | 5 MB | 5 MB | 10 MB | 5 MB attachments | — |
| Account expires | No | No | Namespace dies after 1 month | No | — |
| Receiving mail | |||||
| Point your app at a real SMTP endpoint | SMTP + AUTH, any RCPT TO | SMTP credentials per sandbox | Receive-only *@ns.mailisk.net | SMTP credentials per sandbox | Generated addresses |
| Catch-all recipients | Yes | Yes | Unlimited addresses | Yes | One address per inbox |
| External services can mail you | No public MX | Paid plans only | Yes | Yes | Yes |
| Automation & testing | |||||
| Read mail via REST API | Read-only CI token | Yes | Full API + SDKs | Yes | Full API + SDKs |
| IMAP & POP3 access | Both | No | No | No | No |
| Webhooks on new mail | SES-style SNS events | — | Poll the API instead | Yes | Rules + webhooks |
| Delivery simulation | bounce, complaint, reject, deferral, drop | Bounce simulation | No | — | — |
| Live inbox updates | SSE push | Auto-refresh | — | — | — |
| Team & access | |||||
| Team members | Share mailboxes with members | 1 user | Unlimited | 1 member | 1 user |
| Forward mail to a real inbox | To owner/member addresses | Paid plans only | No | — | — |
| Sign-up | Google / GitHub OAuth, no card | Account, no card | Account, no card | Account, no card | Account, no card |
Which one should you pick?
- Mail Blackhole: The only free tier with no monthly send cap — limits are per-mailbox storage, so heavy CI suites do not run dry mid-month. Also the only one with IMAP/POP3, SES-style bounce/complaint simulation and SNS webhooks. Best when you want a real SMTP endpoint to relay through.
- Mailtrap: The most polished sandbox UI with spam-score checks, but the free tier is the tightest here: 50 emails a month and only 10 stored messages. Fine for occasional manual checks.
- Mailisk: Unlimited addresses under one subdomain and a Playwright/Cypress-first API — great for E2E signup flows where your app mails a real address. Emails vanish after 1 day and there is no SMTP relay endpoint.
- Mailloop: 500 emails a month plus 20 email-client previews, EU-hosted. A good Mailtrap-style sandbox when you also want rendering checks and can live inside the monthly cap.
- MailSlurp: API-first with SDKs in many languages, real email addresses, SMS and phone numbers on paid plans. Free external sending is blocked, and reading mail goes through the API — no IMAP.
Limits taken from each product's public pricing and documentation pages, October 2026. Free tiers change often — check the vendor's site before deciding.
About Mail Blackhole Comparison
A side-by-side look at the free tiers of Mailtrap, Mailisk, Mailloop and MailSlurp next to our own Mail Blackhole mailboxes — monthly email quotas, inbox counts, retention windows, API access and extras like IMAP, webhooks and bounce simulation.
Most free plans cap you at 50–500 emails a month. Mail Blackhole has no monthly cap at all: each of your 10 mailboxes stores up to 100 messages and 50 MB with 30-day retention, readable in the browser, over IMAP/POP3, or through a read-only REST API token built for CI. Figures come from each vendor's public pricing pages and change over time.