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Sendmail makes my head hurt    [ Software ]

Yes, I know, it's the default MTA on most vendor's Unix-style systems, and it's configurable to do anything you could ever want to do with email.   Including pre-processing it for transmission over a UUCP link as an EBCDIC representation of 40-year-old punchcards.   God only knows why you would want to do this, but sendmail lets you do it.

Perhaps that's the problem.   Sendmail lets you do this only after you've twisted your brain around configuration directives that make Obfuscated Perl or C Code look like excerpts from page 10 on BASIC for Dummies.   To quote from section 16.4 of the Bat Book:

Note that this new client.cf file added the name of the hub to the lone username
in the last line, whereas our original client.cf did not. To see why this happened,
first look for rule set 3 in this new client.cf file. It contains the line
R$+ @ $=w               $@ $1 @ $M                      ...@thishost
Next look in the original client.cf file. It contains a similar rule:
R$- @ $=w              $@ $1@${HUB}            user@local -> user@hub
But the original client.cf file put this rule in rule set Hubset. The new client.cf
adds the hub's name to a lone username in rule set 3 that affects all addresses,
while old client.cf file adds it in the S= rule set, which affects only sender addresses.

Bleaaarghh!   What the bloody 'ell is R$+ and R$-?   The syntax makes my head hurt even after I read through it three times, and this is from an excellent book by excellent authors from an excellent publishing house.   This is why I like postfix so much better.