What’s a “bounce signature” and why is it useful?
A bounce signature uniquely identifies a bounce type:
What comprises a signature:
SMTP response code. Enhanced status code. Key phrases in diagnostic text. Provider or MTA identifier.
Signature examples:
Gmail user unknown: 550 5.1.1 + "does not exist" + mx.google.com. Microsoft rate limit: 421 + RP-001 + outlook.com MX. Generic full mailbox: 552 5.2.2 + "mailbox full."
Why signatures are useful:
Consistent classification across occurrences. Machine-readable categorization. Dictionary building and maintenance. Pattern matching automation.
Building a signature library:
Collect bounce samples. Extract key identifying elements. Create matching rules. Test and refine.
Signatures are fingerprints for bounces. They enable reliable identification and handling.
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