Why We Built This
Testing email deliverability is often a frustrating cycle. Standard diagnostics tools have a major limitation: they only allow you to send a single email per generated address.
If you want to test and compare how Google Workspace, Microsoft 365, and your transactional SMTP provider (like SendGrid or Mailgun) authenticate, you are forced to generate three separate test addresses, send three separate emails, and keep track of three separate browser tabs to compare the results.
ONE Address. Multiple Emails. Full Clarity.
We solved this. TestOneMail gives you ONE test address to send multiple emails to. All incoming diagnostics are grouped side-by-side using real-time WebSockets, allowing you to compare providers, detect alignment discrepancies, and resolve deliverability bottlenecks — all from that ONE address, in a single clean view.
Core Capabilities
- Side-by-Side Comparison: Compare SPF, DKIM, and DMARC alignment from different sending sources on a single test page.
- Real-Time Stream: Thanks to integrated WebSocket push notifications, reports update on your screen instantly as soon as the email reaches our MTA.
- Standards‑Compliant Authentication Checks: Real verification of SPF records, DKIM cryptographic signatures, and DMARC policy alignment.
- IPv4 Blocklist Screening: Checks the sending mail server IP against 23 of the most common DNS-based blocklists (DNSBL) including Spamhaus, Barracuda, SORBS, and SPAMCOP.
- Persistent Shareable Links: Copy the unique report URL and share it directly with mail engineers or security teams.
How It Works
Generate ONE unique address at 1.testonemail.com, send one or more emails to it from any provider, and watch the full SPF, DKIM, DMARC, and blocklist diagnostic reports arrive in real time. No account required, no paywalls, no limits.
Looking Ahead
TestOneMail is a free, lightweight, open-source email authentication diagnostic tool available at testonemail.com. As we continue to expand features (such as content-spam scoring and advanced DNS validation tests), we aim to remain the simplest, fastest, and most transparent alternative for engineers who need to verify their email infrastructure.