@vindex mm-coding-system-priorities
Prioritize coding systems to use for outgoing messages. The default
is @code{nil}, which means to use the defaults in Emacs. It is a list of
-coding system symbols (aliases of coding systems does not work, use
-@kbd{M-x describe-coding-system} to make sure you are not specifying
-an alias in this variable). For example, if you have configured Emacs
+coding system symbols (aliases of coding systems are also allowed, use
+@kbd{M-x describe-coding-system} to make sure you are specifying correct
+coding system names). For example, if you have configured Emacs
to prefer UTF-8, but wish that outgoing messages should be sent in
ISO-8859-1 if possible, you can set this variable to
-@code{(iso-latin-1)}. You can override this setting on a per-message
+@code{(iso-8859-1)}. You can override this setting on a per-message
basis by using the @code{charset} @acronym{MML} tag (@pxref{MML Definition}).
@item mm-content-transfer-encoding-defaults
(digitally signed messages require 7bit encoding). Besides the normal
@acronym{MIME} encodings, @code{qp-or-base64} may be used to indicate that for
each case the most efficient of quoted-printable and base64 should be
-used. You can override this setting on a per-message basis by using
-the @code{encoding} @acronym{MML} tag (@pxref{MML Definition}).
+used.
+
+@code{qp-or-base64} has another effect. It will fold long lines so that
+MIME parts may not be broken by MTA. So do @code{quoted-printable} and
+@code{base64}.
+
+Note that it affects body encoding only when a part is a raw forwarded
+message (which will be made by @code{gnus-summary-mail-forward} with the
+arg 2 for example) or is neither the @samp{text/*} type nor the
+@samp{message/*} type. Even though in those cases, you can override
+this setting on a per-message basis by using the @code{encoding}
+@acronym{MML} tag (@pxref{MML Definition}).
@item mm-use-ultra-safe-encoding
@vindex mm-use-ultra-safe-encoding