What’s the difference between internal and external routing?

Internal routing handles mail that stays within your organization. Messages between employees, system notifications to internal addresses, and intranet communications. This traffic often bypasses internet-facing infrastructure, moving directly between internal servers.

External routing involves mail leaving your network for outside recipients. It requires DNS lookups to find recipient mail servers, TLS negotiation for secure transmission, and authentication records that external servers can verify. External mail passes through your outbound gateway or ESP.

Many organizations maintain separate paths for internal and external mail. Internal routing prioritizes speed and availability; external routing emphasizes authentication, reputation, and compliance. Security policies often differ too: internal mail may skip certain spam checks while external mail receives full filtering.

Harbor traffic moves freely within the port. Ships leaving for open water get inspected at the exit.