+# 3.182. message_id_format
+#
+# Type: string
+# Default: “<%z@%f>”
+#
+# This variable describes the format of the Message-ID generated when sending
+# messages. Mutt 2.0 introduced a more compact format, but this variable allows
+# the ability to choose your own format. The value may end in “|” to invoke an
+# external filter. See formatstrings-filters.
+#
+# Please note that the Message-ID value follows a strict syntax, and you are
+# responsible for ensuring correctness if you change this from the default. In
+# particular, the value must follow the syntax in RFC 5322: “"<" id-left "@"
+# id-right ">"”. No spaces are allowed, and id-left should follow the
+# dot-atom-text syntax in the RFC. The id-right should generally be left at %f.
+#
+# The old Message-ID format can be used by setting this to: “
+# <%Y%02m%02d%02H%02M%02S.G%c%p@%f>”
+#
+# The following printf(3)-style sequences are understood:
+#
+# ┌──┬─────────────────────────────────────────────────────────────────┐
+# │%c│step counter looping from “A” to “Z” │
+# ├──┼─────────────────────────────────────────────────────────────────┤
+# │%d│current day of the month (GMT) │
+# ├──┼─────────────────────────────────────────────────────────────────┤
+# │%f│$hostname │
+# ├──┼─────────────────────────────────────────────────────────────────┤
+# │%H│current hour using a 24-hour clock (GMT) │
+# ├──┼─────────────────────────────────────────────────────────────────┤
+# │%m│current month number (GMT) │
+# ├──┼─────────────────────────────────────────────────────────────────┤
+# │%M│current minute of the hour (GMT) │
+# ├──┼─────────────────────────────────────────────────────────────────┤
+# │%p│pid of the running mutt process │
+# ├──┼─────────────────────────────────────────────────────────────────┤
+# │%r│3 bytes of pseudorandom data encoded in Base64 │
+# ├──┼─────────────────────────────────────────────────────────────────┤
+# │%S│current second of the minute (GMT) │
+# ├──┼─────────────────────────────────────────────────────────────────┤
+# │%x│1 byte of pseudorandom data hex encoded (example: '1b') │
+# ├──┼─────────────────────────────────────────────────────────────────┤
+# │%Y│current year using 4 digits (GMT) │
+# ├──┼─────────────────────────────────────────────────────────────────┤
+# │%z│4 byte timestamp + 8 bytes of pseudorandom data encoded in Base64│
+# └──┴─────────────────────────────────────────────────────────────────┘
+#
+
+
+# 3.183. meta_key