Are bounce codes standardized across the industry?

Bounce code standardization: Partial.

What is standardized:

Basic SMTP codes: RFC 5321 defines 2xx, 4xx, 5xx. Enhanced codes: RFC 3463 defines X.Y.Z format. DSN format: RFC 3464 structures bounce messages.

What is not standardized:

Specific message text. Provider-specific sub-codes (RP-001). Custom error identifiers. Interpretation of ambiguous cases.

Practical reality:

Major providers follow standards loosely. Add proprietary extensions. May use same code for different meanings. Message text varies widely.

Handling approach:

Use standards as baseline. Build provider-specific rules. Maintain flexible parsing. Update as providers change.

Standards provide foundation; reality adds complexity. Expect variation and adapt.