What this code means
The specified recipient mailbox address was found to be valid. This is a success confirmation, not a message rejection.
Technical meaning
Code X.1.5 means that the mailbox address specified as the destination was valid. The standard provides this code for positive delivery reports.
Delivery status
The leading digit 2 denotes success. Code 2.1.5 does not describe an error or rejection; it confirms address validity in a positive delivery report.
- Class
- Success
- Retry
- Do not retry unchanged
- Suppression
- Check the full context
Retry decision
Do not retry because of code 2.1.5 alone, since it does not indicate a failure that needs another attempt. If the expected outcome is not visible, inspect the remaining events for this message.
Suppression decision
Do not decide to add the address to a suppression list based on code 2.1.5 alone. Evaluate the full message context and any later events before changing the recipient's state.
Common causes
- The reporting system confirmed that the specified destination mailbox address is valid.
- A positive delivery report was generated for the message with this addressing status code.
Diagnostic steps
- Confirm that the parsed enhanced code is exactly 2.1.5 and that it comes from the report for the intended message.
- Check the message identifier and timestamps to correlate the report with the specific send attempt.
- Review later message events if you need to establish its final state beyond the address-validity confirmation itself.
Actions by owner
Sender
- Treat this code as a successful address check and do not resend solely because it appeared.
- Retain the report with the message history so that subsequent events can be interpreted correctly.
Sender administrator
- Ensure the event classifier recognizes class 2 as success rather than rejection.
- Do not trigger automatic suppression for 2.1.5 without evaluating other events and recipient rules.
Sources and verification
The code meaning and class come from the IANA registry and the associated RFC 2034, RFC 3463, and RFC 5248 documents, verified on July 17, 2026. The retry, suppression, diagnostic, and owner-action recommendations are separate operational guidance, not facts from the standard or a provider.
- iana-smtp-enhanced-status-codesT0 source
Enumerated Status Codes / X.1.5
- rfc5248T0 source
Section 2.1: registry fields and non-exclusive Associated Basic Status Code
- rfc2034T0 source
Section 4: enhanced status class agrees with SMTP reply class
- rfc3463T0 source
IANA registry reference for X.1.5
Last verified:
