UUCP with qmail and later Postfix was a great way to shove e-mail over these really unreliable connections. The g protocol worked amazingly well over these unreliable connections because it could pick up where it left off, so as long as you could get a few packets through, eventually your (sometimes large) e-mail messages could make it through, even if they had the spend the night trying.
The company kept that architecture well into the 2010s, even when we all had fairly speedy, reliable Internet connections, because it just worked really well. They eventually went to gmail years after I left.
UUCP had it's issues, but it was (and still is) one of the best was to transfer stuff over really bad connections. We worked at a place where we had really remote locations and UUCP stuff worked without much work.
Plus, I learned a ton in writing something to do reports and monitoring of the UUCP connections. Fun times, but I am still scarred Sendmail. Some wounds are pretty deep.
I had recommended they switch to using Taylor UUCP, because it splits the queue directory up into a hierarchy. They said Taylor wasn't mature enough, but I asked Ian Lance Taylor about it and he laughed and said "<THE major commercial UUCP provider> doesn't seem to agree." :-)
I've always heard that Kermit has really great protocols for handling horribly, horribly bad modem connections. I had at times wondered if a kermit UUCP protocol would have been useful.
I use to be a Sendmail consultant.
I've seen things you people won't believe. Open SMTP relays with zero firewall protection. I've watched people use sendmail to get root without a password. I've seen volumes of email lost in time, like bits into /dev/null. Time to patch.