+@item nnimap-nov-is-evil
+@vindex nnimap-nov-is-evil
+@cindex Courier @acronym{IMAP} server
+@cindex @acronym{NOV}
+
+Never generate or use a local @acronym{NOV} database. Defaults to the
+value of @code{gnus-agent}.
+
+Using a @acronym{NOV} database usually makes header fetching much
+faster, but it uses the @code{UID SEARCH UID} command, which is very
+slow on some servers (notably some versions of Courier). Since the Gnus
+Agent caches the information in the @acronym{NOV} database without using
+the slow command, this variable defaults to true if the Agent is in use,
+and false otherwise.
+
+@item nnimap-search-uids-not-since-is-evil
+@vindex nnimap-search-uids-not-since-is-evil
+@cindex Courier @acronym{IMAP} server
+@cindex expiring @acronym{IMAP} mail
+
+Avoid the @code{UID SEARCH UID @var{message numbers} NOT SINCE
+@var{date}} command, which is slow on some @acronym{IMAP} servers
+(notably, some versions of Courier). Instead, use @code{UID SEARCH SINCE
+@var{date}} and prune the list of expirable articles within Gnus.
+
+When Gnus expires your mail (@pxref{Expiring Mail}), it starts with a
+list of expirable articles and asks the IMAP server questions like ``Of
+these articles, which ones are older than a week?'' While this seems
+like a perfectly reasonable question, some IMAP servers take a long time
+to answer it, since they seemingly go looking into every old article to
+see if it is one of the expirable ones. Curiously, the question ``Of
+@emph{all} articles, which ones are newer than a week?'' seems to be
+much faster to answer, so setting this variable causes Gnus to ask this
+question and figure out the answer to the real question itself.
+
+This problem can really sneak up on you: when you first configure Gnus,
+everything works fine, but once you accumulate a couple thousand
+messages, you start cursing Gnus for being so slow. On the other hand,
+if you get a lot of email within a week, setting this variable will
+cause a lot of network traffic between Gnus and the IMAP server.
+