What are some known specific bounce messages from Outlook?

Microsoft Outlook/365 uses distinctive error formats:

Rate limiting codes:

"421 RP-001" through "421 RP-003": Various rate limit types. "421 4.7.0 Connection rate limit exceeded."

User-related codes:

"550 5.1.1 User unknown." "550 5.1.10 Recipient not found." "550 5.2.1 Mailbox disabled."

Policy and reputation:

"550 5.7.1 Service unavailable, client host blocked." "550 5.7.606 Access denied, banned sending IP." "550 5.7.708 Access denied, traffic not accepted from this IP."

Storage and limits:

"550 5.2.2 Mailbox full." "550 5.3.4 Message size exceeds limits."

Characteristic features:

Alphanumeric sub-codes (RP-001). Detailed 5.7.xxx policy codes. References to sender.office.com.

Microsoft provides structured codes for programmatic parsing. Learn the RP-series and 5.7.xxx codes.