What’s the difference between local and remote bounce sources?

Local vs remote bounce sources indicate different problems:

Local bounce sources:

Your sending server. Your MTA queue. Your relay infrastructure. Before external transmission.

Local causes:

Configuration errors. DNS lookup failures from your end. Queue expiration. Internal policy rejections.

Remote bounce sources:

Recipient's MX server. Intermediate relays. Gateway security services. After leaving your network.

Remote causes:

User does not exist. Mailbox full. Reputation rejection. Content filtering.

Diagnostic difference:

Local: You can fix it. Remote: Depends on external factors. Identifying source determines response.

Local bounces are your ship's problems. Remote bounces are the destination's decisions.