It appears that several versions of sendmail require that the mail is sent to them with
LF line endings instead of CRLF endings - which of course they will then convert back
to CRLF line endings to comply with the SMTP standard.
This PR adds another setting SENDMAIL_CONVERT_CRLF which will pass the message writer
through a filter. This will filter out and convert CRLFs to LFs before writing them
out to sendmail.
Fix#18024
Signed-off-by: Andrew Thornton <art27@cantab.net>
1514e13bb8