As far as I know, there are only three possible results of sendmail running:

    0: It happened.

    255: The sendmail binary failed to execute. (This value may be OS-dependent.)

    other nonzero value: You failed to pass in a recipient parameter.

So it might be worth checking the exit status to catch mistakes caused by somebody entering 
the wrong path for the sendmail binary, or passing a sendmail binary that won't execute for 
some reason or whatever.

Beyond that, though, sendmail does basically zero validity checking.  You can pass in 
complete gibberish (and possibly even an empty string) for the recipient address, and 
complete gibberish for the message, and it still exits successfully, as far as I can tell.  So for 
the most part, it's a "hand it off and hope" technique.  If it fails, you'll know it when you get a 
bounce message in the inbox of the person listed in the From: field.  :-)


As for documentation, presumably the new key in the config file would need to be explained 
in the config file, e.g.

"sendmail: The path to a local sendmail binary.  If nonempty, the specified binary is used for 
handling all mail delivery, and any SMTP hostname and port settings are ignored."

Or the equivalent info in a form that conforms to your house style.

Also, it would probably be worth adding a section to the "Installing Roundup" document to 
cover setting up outgoing email.  Right now, I'm not seeing that mentioned at all, and if you 
don't do that, you can easily find yourself locked out of accounts because it can't send out 
password change emails.