nnimap.el: Handle plain value for nnimap-stream

* lisp/gnus/nnimap.el (nnimap-open-connection-1): Always query
capabilities, so that a 'plain value for the `nnimap-stream' server
variable is handled correctly.

* doc/misc/gnus.texi (Customizing the IMAP Connection):
Document the 'plain option.

2 files changed, 5 insertions, 0 deletions

diff --git a/doc/misc/gnus.texi b/doc/misc/gnus.texi
index d801031c563..0afc7e47c4b 100644
--- a/doc/misc/gnus.texi
+++ b/doc/misc/gnus.texi
@@ -14252,6 +14252,10 @@ If you need to tunnel via other systems to connect to the server, you
 can use this option, and customize @code{nnimap-shell-program} to be
 what you need.
 
+@item plain
+Non-encrypted and unsafe straight socket connection.
+@acronym{STARTTLS} will not be used even if it is available.
+
 @end table
 
 @item nnimap-authenticator
diff --git a/lisp/gnus/nnimap.el b/lisp/gnus/nnimap.el
index 40610e1d71a..8eb6268a140 100644
--- a/lisp/gnus/nnimap.el
+++ b/lisp/gnus/nnimap.el
@@ -423,6 +423,7 @@ textual parts.")
                :return-list t
                :shell-command nnimap-shell-program
                :capability-command "1 CAPABILITY\r\n"
+               :always-query-capabilities t
                :end-of-command "\r\n"
                :success " OK "
                :starttls-function