nnimap.el: support additional expunge options

* lisp/gnus/nnimap.el (nnimap-close-group)
(nnimap-request-expire-articles, nnimap-delete-article)
(nnimap-request-scan): add new 'never, 'immediate, and 'on-exit
settings for nnimap-expunge (bug#20670).

1 files changed, 10 insertions, 0 deletions

diff --git a/etc/NEWS b/etc/NEWS
index ca66df62610..e5ee40cbe4b 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -81,6 +81,16 @@ for '--daemon'.
 * Changes in Emacs 26.1
 
 +++
+** The Gnus user variable 'nnimap-expunge' supports three new values:
+'never' for never expunging messages, 'immediately' for immediately
+expunging deleted messages, and 'on-exit' to expunge deleted articles
+when exiting the group's summary buffer. Setting 'nnimap-expunge' to
+'nil' or 't' is still supported but not recommended, since it may
+result in Gnus expunging all messages that have been flagged as
+deleted by any IMAP client (rather than just those that have been
+deleted by Gnus).
+
++++
 ** The new function 'mapbacktrace' applies a function to all frames of
 the current stack trace.