Version 4.02
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 1. If a message body contains binary zero characters, they are turned into
    spaces when the contents of the body are copied into the $message_body and
    $message_body_end variables. Otherwise, they cause premature termination of
    the strings.

 2. The helo_allow_chars option can be set to a string of rogue characters
    that are permitted in all HELO/EHLO names in addition to the standard
    letters, digits, hyphens, and dots. So if you really must allow
    underscores, you can set

      helo_allow_chars = "_"

    Note that it is one string, not a list.

 3. In the mysql_servers data, the format for the "hostname" field has been
    extended to allow for the specification of an alternate Unix domain socket.
    The full syntax of each item in mysql_servers is now:

      hostname::port(/socket/name)/database/user/password

    Any of the three sub-parts of the first field can be omitted. For normal
    use on the local host it can be left blank or set to just "localhost".

 4. If tls_certificate is set, but tls_privatekey is not set, the file named by
    tls_certificate is used for tls_privatekey.

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