What are typical Gmail vs Microsoft error code patterns?

Major providers have distinct error code patterns:

Gmail patterns:

Uses standard SMTP codes with detailed text. Includes reason strings: "Our system has detected..." References documentation: "Please visit support.google.com..." Examples: "550-5.1.1 The email account does not exist."

Microsoft (Outlook/365) patterns:

Uses alphanumeric sub-codes: "421 RP-001" for rate limiting. Specific enhanced codes: 5.1.0, 5.2.2, 5.7.1 with custom meanings. References NDR error codes in documentation.

Yahoo patterns:

Often uses "deferred" messaging. Policy rejection messages reference complaints. TS01, TS02, TS03 style codes for throttling.

Practical approach:

Maintain provider-specific parsing rules. Reference each provider's postmaster documentation. Track patterns that emerge from your own sending.

Each major provider speaks a slightly different dialect. Learn to interpret each one.