SMTP status interpretation
Email Bounce Code Analyzer
Extract standard three-digit and enhanced status codes from a server diagnostic, then separate temporary and permanent responses without inventing a cause.
Enhanced status codes
Codes such as 5.1.1 or 4.2.2 have three parts: success class, subject, and detail. The first digit distinguishes success (2), persistent transient failure (4), and permanent failure (5). The remaining digits narrow the category.
Use the receiver's text carefully
Diagnostic text is supplied by a receiving system and varies. Preserve the original event for support, but do not generalize one response into an address-quality or deliverability claim beyond that attempted delivery.
Choose retry behavior deliberately
Queue and retry temporary responses with bounded backoff. Permanent responses normally should not be retried unchanged. Suppress recipients only under a documented policy and retain a safe review path for ambiguous provider responses.
Questions about this tool
Is every 550 response an invalid address?
No. 550 is a permanent SMTP response, but the underlying reason can involve addressing, policy, content, authentication, or another condition. Use the enhanced code and server text.
Should a 4xx response be retried?
It is a transient class, so bounded retries can be appropriate. Respect provider retry guidance and avoid creating duplicate application jobs.
Does a bounce prove an address never existed?
No. It records the receiving system's result for a particular attempt and time.