+New "control = utf8_downconvert" ACL modifier,
+sets a flag requiring that addresses are converted to
+a-label form before smtp delivery, for use in a
+Message Submission Agent context. Can also be
+phrased as "control = utf8_downconvert/1" and is
+mandatory. The flag defaults to zero and can be cleared
+by "control = utf8_downconvert/0". The value "-1"
+may also be used, to use a-label for only if the
+destination host does not support SMTPUTF8.
+
+If mua_wrapper is set, the utf8_downconvert control
+defaults to -1 (convert if needed).
+
+
+There is no explicit support for VRFY and EXPN.
+Configurations supporting these should inspect
+$smtp_command_argument for an SMTPUTF8 argument.
+
+There is no support for LMTP on Unix sockets.
+Using the "lmtp" protocol option on an smtp transport,
+for LMTP over TCP, should work as expected.
+
+Known issues:
+ - DSN unitext handling is not present
+ - no provision for converting logging from or to UTF-8