Friend at Yale was a bang-path email relay in 1987. Can't remember the structure, the actual address or how it worked.
p293 " ! Should only be used when sending via UUCP. This should be the only special character in the address (called a path). The path indicates each site through which mail will be routed, starting at the left and going towards the right. Mixing ! with @ is not considered good. That is, use:
uunet!ucbvax.berkeley.edu.edu!smith
not:
uunet!smith@ucbvax.berkeley.edu.edu"
In other words because UUCP was dialup and long distance expensive, email was routed through specific known hosts, which is why sometimes people ended up with long bangpathed addresses.