[exim] Number of header lines in reject log

Hi All

Our exim reject log files include headers of rejected messages. This is
useful as when we receive a report of a "false positive" rejection from
our anti-spam or anti-virus filters, we can find the logs and work out
what happened and if necessary modify the filters or whitelist something.

However exim has a limit on the number of header lines that are written
into the reject log, if the number of headers exceed this the log is
truncated. We find that some senders, like Outlook 365, include many
lines of proprietary headers. This adds to the number of lines getting
logged and the log can get truncated before lines added by our spam
assassin filter are written to the log. This makes debugging the false
positive more challenging.

Is there a setting which allows one to increase the number of header
lines logged, before the log is truncated? I cannot find any relevant
setting in the documentation.

Thanks

Ian