One of my first email addresses (in 1989) was tektronix!ogicse!reed!minar. I’m feeling old today and I’m guessing half my readers have never seen an email address like that. It was from the long long ago, in the time that was before the Internet, when UUCP was the main Unix mail system.
My unique email address was reed!minar. But there was no ubiquitous routing infrastructure for mail, no global addressing. Unix network email was store-and-forward based on scheduled phone calls and modem transfers via uucico. Each host only talked to a few other hosts. Reed talked to OGICSE regularly, so my address suggested mail be forwarded through there. Other mail hosts might or might not know how to get mail to OGI but they certainly knew how to get to Tektronix, so that sufficed as a global route. UUNET was a hub that knew how to talk to everyone; often addresses began uunet!.
The essential idea is that UUCP email addresses included not just the address but the route to that address. It's a powerful idea. But modern Internet systems don’t do that. Instead we rely on global address lookup systems like DNS and global routing systems like BGP. (If anyone can think of a modern system that includes routes in names, please email me via SMTP)
UUCP users did build a routing system; pathalias. It relied on UUCP maps published to comp.mail.maps. Those maps were discontinued in December 2000. I haven’t found a modern view onto this data; it’d be fascinating to see the history of the growth of UUCPnet. telehack has a usable snapshot of the data, try uumap reed for instance.