set transient response code on potential temporary error conditions #209
Conversation
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
decke
approved these changes
May 16, 2025
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
Unkown errors may be caused by temporary error conditions, e.g. socket errors (DNS errors, network interruptions, ...), but smtprelay responds with a final SMTP error code. Since final SMTP error codes leads to a different behavior of correct working clients (bounce instead of retry), a 5xx response signals clients to give up on a specific mail instead of retrying a later delivery. This is not correct for temporary error conditions, so smtprelay should respond with a 4xx transient error code.
I think SMTP error code 421 is a more proper response for unkown conditions, that prevents smtprelay to forward an mail.
https://www.cloudmailin.com/smtp-troubleshooter/421-error