Why is UUCP Notoriously Unreliable?

[johnl at ima.UUCP]

Running out of disk space is certainly the most common reason to lose uucp
traffic (it happens here at ima all the time.)  Another big problem is that
most versions of uucp do nothing useful when they cannot contact a remote
host for a long time -- the version here usually sends a cryptic message
about "cannot contact host, deleting C.floogleA1234" to root or uucp, but
there's no hint to the original sender four hops back where the problem is.

John Levine, ima!johnl

PS:  There are versions that fix this other problem, since at least one
host, ihnp4, is very good about sending back mail that it can't deliver
for a week.