Netscape on Unix is sending messages containing an unqualified user name in the Sender: header line, which Exim is rejecting because I have set verify = header_syntax. How can I fix this?

The only thing you can do in Exim is to set the sender_unqualified_hosts option to allow unqualified sender addresses form the relevant hosts; of course, this applies to all sender addresses, not just the Sender: header line. Alternatively, you can configure Netscape not to include the header line in the first place. Add the following line to the $HOME/.netscape/preferences.js and $HOME/.netscape/liprefs.js files:

user_pref("mail.suppress_sender_header", true);

Netscape must be shut down while doing this.