I didn't need to most times to send mail, the sendmail program would rewrite the paths. Sure, you could use bang routing.
An old BBS I had was listed with this info: 1200/2400 bps, (Uucp: sma2), Sysop email: (...!m2xenix!sma2!root)

In the end before UUCP services with dropped locally, I used UUCP over TCP to maintain the old system.
https://tldp.org/LDP/nag/node168.html
https://www.postfix.org/UUCP_README.html

Bang routing was the funnest part of UUCP. For a little while I ran IPv6 Archie and Veronica servers... just remembering...

 

No its not , I just woke up today and decided to try to build a new internet.

Reminds me, in a good way, that 1970s song.