Test whether any email address or bulk CSV / Excel (.XLSX) list will return a 550 Hard Bounce before you hit send. Our non-intrusive 7-Layer Smart SMTP handshake checks mailbox existence without sending an email.
Pre-scan your list for hard bounces, dead domains, and disposable traps + test 5 emails live via SMTP.
See how much you save on email bounce checker from 5,000 to 100,000 contacts with KaijuVerifier:
| Email Bounce Checker Provider | 5k Tier (Email Bounce Checker) | 10k Tier | 50k Tier | Unknowns Policy | Excel .XLSX Support |
|---|---|---|---|---|---|
| ⚡ KaijuVerifier (Email Bounce Checker) | $19 (Never Expires) | $19/mo (Rollover) | $49/mo (Save 88%) | ✅ $0 (100% Free) | ✅ Native Multi-Tab |
| ZeroBounce | $45 | $99 | $390 | ❌ Charged | ❌ CSV only |
| NeverBounce | $40 | $50 | $250 | ❌ Charged | ❌ CSV only |
| Bouncer (UseBouncer) | $40 | $60 | $250 | ✅ Refunded | ❌ CSV only |
| Emailable | $38 | $60 | $225 | ✅ Refunded | ❌ CSV only |
| EmailListVerify | $15 | $27 | $169 | ⚠️ Manual ticket | ⚠️ Single-sheet |
Under Gmail, Yahoo, and Microsoft 365 bulk-sender enforcement rules, a hard bounce rate above 2% triggers automatic spam-folder routing or ESP suspension. Our Email Bounce Checker simulates the exact SMTP delivery handshake up to RCPT TO:
Connects to the recipient MX server over port 25 and checks the exact SMTP status code for the target mailbox, disconnecting cleanly before DATA.
Distinguishes true deliverable inboxes from accept-all corporate gateways and temporary 421/450 soft-bounce deferrals.
If a mail server temporarily defers the bounce check, you pay $0. Unlock 5,000 bounce checks for $19 (credits never expire).
Our email bounce checker resolves the domain’s MX records, establishes an SMTP session (EHLO / MAIL FROM / RCPT TO), reads the server’s 250 OK or 550 User Unknown response, and issues RSET + QUIT before any message body is transmitted.
Yes. Drop your CSV, TXT, or Multi-Sheet Excel (.XLSX) file into the Bulk Email List Bounce Checker above to pre-scan your entire list and isolate every hard bounce in minutes.
Our Pre-Send Email Bounce Checker (550 / 554 / 421) is built around Non-Intrusive SMTP RCPT TO Diagnostic, focused on Detecting permanent 550 User Unknown hard bounces without sending mail. Every check runs across our 7 distributed verification clusters with full TLS 1.3 security and zero data retention.
Unlike generic bulk tools that charge for duplicate rows or inconclusive timeouts, this workflow combines browser-native pre-scanning ($0 cost for duplicates and syntax errors) with live 7-Layer Smart SMTP verification starting at $19 for 5,000 non-expiring credits.
| Technical Dimension | Specification (Non-Intrusive SMTP RCPT TO Diagnostic) | Operational Outcome |
|---|---|---|
| Primary Architecture | Non-Intrusive SMTP RCPT TO Diagnostic | Detecting permanent 550 User Unknown hard bounces without sending mail |
| Accuracy & Unknown Policy | 99.7% Definitive SMTP Precision | $0 charged for Unknown, Greylisted, or Duplicate rows |
| Supported Formats & API | CSV, TXT, .XLS, Multi-Sheet .XLSX & REST API | 100 free monthly checks + non-expiring Pay-As-You-Go packs |