-Takes a MIME::Header object. Returns a tuple: (user@host, friendly name)
-of the From (evaluated in order of Reply-To:, From:, Sender)
+Takes a MIME::Header object. Returns (user@host, friendly name, errors)
+where the first two values are the From (evaluated in order of
+Reply-To:, From:, Sender).
+
+A list of error messages may be returned even when a Sender value is
+found, since it could be a parse error for another (checked earlier)
+sender field. In this case, the errors aren't fatal, but may be useful
+to investigate the parse failure.