Log Message:
Update to 2.1. From the changelog:

- Added support for TLS anonymous authentication.
  Thanks Uffe Jakobsen.
- Fixed sendmail wrapper handling of empty sender on command line.
  Thanks Sebastian Wiedenroth.
- Fixed handling of quoted strings in the "remotes" file.
  Thanks Mihai Moldovan.
- Fixed nullmailer-inject handling of leading "From " lines.
- Some build fixes.
- Fixed bogus temporary gethostbyname error message when the protocol
  source address was incorrect.
- Fixed potential race condition in tests.
  Thanks Felix Lechner.
- Fixed handling of time values on 32-bit big-endian systems.
  Thanks Felix Lechner.
- Added support to nullmailer-send to move permanently failing messages
  out of the queue, and to generate bounce messages.
- Added support for IPv6.
- Added program to generate bounce/delay messages.
- Added an "allmailfrom" control file to nullmailer-queue, causing all
  messages to share a hard-coded envelope sender.
- Added logging the message sender/recipient in nullmailer-send.
- Improved handling of system errors when reading config files.
- Secured handling of password options for protocol modules.
- Support standard shell quoting for options in the "remotes" file.
- Added protocol option to set a separate TLS client private key file.
- Added protocol option to bind the source address on connections.
- Fixed nullmailer-inject to report errors to stderr.
- Fixed gnutls cast to pointer from integer of different size warning.
- Fixed nullmailer-inject and -queue to handle the null (empty) sender
  address. Needed for RFC 3798 (Message Disposition Notification).
- Moved spool directory to /var/spool/nullmailer like other MTAs.