  o Finish the TLS code.  
    * client certificate handling.
    * load trusted CAs.
    * hook to SASL EXTERNAL authentication mechanism.
    * report server certificate details (esp fingerprint) to application
    * report cipher in use to application.
    * API to specify minimum acceptable security levels.

  o Make header code do line folding at white spaces.

  o Make header code handle Resent-* headers.

  o Make header cocde handle list notation in appropriate recipient headers.

  o Review API.

  o Review error reporting.

  o Loadsa documentation.

