Log Message:
msmtp: Update to 1.8.11

Changelog:
Version 1.8.11:
- Add a new undisclosed_recipients command and --undisclosed-recipients option
  to replace To, Cc, Bcc with a single "To: undisclosed-recipients:;" \ 
header.
- Improved handling of temporary files on Windows systems.
- Re-enabled support for systems lacking vasprintf(), such as IBM i PASE.