Log Message:
Update to version 2.3.1.  From PR#31015 by Julian Dunn.

Here's an excerpt from the rather long RELEASE_NOTES included in the
distribution:

QUICK OVERVIEW:

Provides more flexible configuration of decoders. Allows recipients to have
individual banning rules. Assigns a long-term unique id to each message,
reducing clashes and facilitating retrieval of information. The daemon can
store information to a SQL database for logging, reporting and quarantine
retrieval, optionally storing entire message to a SQL database. File-based
quarantine can disperse files to 62 subdirectories. Provides a quarantine
release mechanism. Reconnects to SQL if connection is broken. Can skip
quarantining high-score spam. Compatibility with IPv6-enabled Postfix
is improved.

SECURITY:

- require minimal version 1.05 of Convert::UUlib to avoid a known security
  problem in the underlying uulib (likely to be exploitable);