That is not actually correct.
in reply to Re^2: Programmatically Adding E-Mail Accounts
in thread Programmatically Adding E-Mail Accounts
Actually, it IS.
The passwd manpage on Linux (Debian) and Solaris do not list the --stdin switch. Quite possibly you are running some system that supports it, but that DOES NOT make what I said incorrect.
The question did not define which operating system the machine he is using actually runs, but it's far more likely that it doesn't support --stdin that that it does.