How does Microsoft classify errors (5.1.0, 5.2.2, 5.7.1)?

Microsoft error classification follows enhanced status code structure:

5.1.x (Address status):

5.1.0: Other address status. 5.1.1: Bad destination mailbox address. 5.1.10: Recipient not found.

5.2.x (Mailbox status):

5.2.1: Mailbox disabled, not accepting messages. 5.2.2: Mailbox full. 5.2.121: Recipient's per-hour message limit exceeded.

5.7.x (Security status):

5.7.1: Delivery not authorized (generic block). 5.7.606: Access denied, banned sending IP. 5.7.708: Access denied, traffic not accepted. 5.7.509: DMARC validation failure.

Reading the structure:

5 = permanent failure. Second digit = category. Third digit = specific condition.

Microsoft's codes are methodical. Learn the category meanings to quickly diagnose issues.