TL;DR
Confirms the recipient mailbox address is valid in a positive delivery report. Important for correlating message events; this is success, not rejection. Do not retry or suppress on this code alone: deliverability and list hygiene are unaffected.
What this code means
When the reporting system treats the destination mailbox address given in the transaction as valid, it reports that reading under addressing pattern X.1.5 in success class 2. Subject family 1 covers mailbox and routing addresses, and the leading digit 2 signals success rather than the temporary or permanent address failures of 4.1.x and 5.1.x. The code usually appears in a positive delivery status report, not as an SMTP rejection reply. It confirms address validity at reporting time, yet the code does not prove final delivery, inbox placement, or that a later rejection will not occur.
Technical meaning
X.1.5 reports that the destination mailbox address was valid. The standard reserves this code for positive delivery status 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
These sources define what this enhanced status code means, mainly through the IANA registry and related RFCs. When provider examples appear on the page, they come from that provider's published documentation. Follow the links to read the original wording in context.
- SMTP Enhanced Status Codes — IANA registry of enhanced mail system status codes.
- RFC 5248 — A Registry for SMTP Enhanced Mail System Status Codes — Creates and governs the IANA enhanced status code registry.
- RFC 2034 — SMTP Service Extension for Returning Enhanced Error Codes — Defines how SMTP returns enhanced status codes to clients.
- RFC 3463 — Enhanced Mail System Status Codes — Defines the class/subject/detail model for enhanced status codes.
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