Route-Based Addressing

Route-based addressing requires the sender of an email message to specify the local address (typically, a user name) and its final destination, as well as the route that the message must take to reach its final destination. Route-based addresses were fairly common on UUCP networks, and have this format:

path!host!user

Whenever you see an exclamation point as part of an email address, all (or some) of the route was specified by the sender. Route-based addresses are always read from left to right.

For example, an email address that looks like this:

venus!acme!sierra!ignatz

means that mail sent to the user named ignatz is first sent to the system named venus, next to acme, and then to sierra. (Notice that this is an example and not an actual route.) If any of the mail handlers is out of commission, the message will be delayed or returned as undeliverable.

Mail sent through the uucp mailer is not restricted to using route-based addressing. Some uucp mailers also handle route-independent addressing.