How do ESPs build bounce dictionaries?

Bounce dictionaries map error patterns to classifications:

Data collection:

Aggregate bounces from millions of sends. Capture full SMTP responses and DSNs. Track across all major providers. Include timestamps and context.

Pattern identification:

Identify common message strings. Map SMTP codes to behaviors. Track provider-specific variations. Detect new patterns as they emerge.

Classification mapping:

Assign categories: hard, soft, block, technical. Determine appropriate actions. Weight confidence levels. Handle ambiguous cases.

Continuous improvement:

Monitor for new error patterns. Update when providers change behavior. Incorporate feedback from false positive detection. Version and test changes.

Dictionary contents:

Regex patterns for message matching. Code-to-category mappings. Provider-specific rules. Confidence scores.

Bounce dictionaries are the Rosetta Stone of email errors. They decode every provider's unique signals.