> It's of course not a production code. I'm only trying to
> learn and understand how exactly it works.
> I cannot find anything about "--" in the postfix documentation
> (or I'm looking on the wrong page?). There is any explanation
> somewhere? (instead of at the source code).
Look at "man getopt" the, i.e. the SYSTEM LIBRARY function that
parses command-line options. Without the '--' before the recipients,
a recipient address starting with '-' would change the way that the
sendmail command works.