bug#24752: 26.0.50; Suppressing unavailable imap server

[Michael Albinus]

I have configured an imap server which is reachable only sometimes (when
I have entered the company's lan). Connecting it via gnus takes always
~2 min, until there is a timeout, and the server is ignored
then("denied" in the *Server* buffer).

I would appreciate if there would be a way to set a status of
"unavailable" to a server. A simple check (a Lisp function provided by
me) shall be possible to deal with this when connecting. And/or there
shall be a simple configuration mean to configure the timeout until a
server is marked as unavailable; 2 minutes is much too long in my case.

Furthermore, this status shall be kept for the whole Emacs session. The
check is not necessary any more, once I have closed and reopened a Gnus
session. If needed, I would reopen the server from the *Server* buffer.

In GNU Emacs 26.0.50.1 (x86_64-pc-linux-gnu, GTK+ Version 2.24.30)
 of 2016-10-01 built on detlef
Repository revision: 4431eff77524c3fb3ac953130081b27cb1a6be7a
System Description:     Ubuntu 16.10

Recent messages:
Auto-saving...done
No more unseen articles
Mark set
Opening nntp server on news.individual.de...done
Returning to the group buffer
Saving /home/albinus/.newsrc.eld...
Saving file /home/albinus/.newsrc.eld...
Wrote /home/albinus/.newsrc.eld
Saving /home/albinus/.newsrc.eld...done
(No changes need to be saved)

Configured using:
 'configure --with-file-notification=inotify'

Configured features:
XPM JPEG TIFF GIF PNG RSVG SOUND GPM DBUS GCONF GSETTINGS NOTIFY GNUTLS
LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB TOOLKIT_SCROLL_BARS GTK2 X11

Important settings:
  value of $LC_MONETARY: de_DE.UTF-8
  value of $LC_NUMERIC: de_DE.UTF-8
  value of $LC_TIME: de_DE.UTF-8
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8

Major mode: Lisp Interaction

Minor modes in effect:
  erc-notify-mode: t
  erc-notifications-mode: t
  erc-list-mode: t
  erc-menu-mode: t
  erc-autojoin-mode: t
  erc-ring-mode: t
  erc-networks-mode: t
  erc-pcomplete-mode: t
  erc-track-mode: t
  erc-match-mode: t
  erc-button-mode: t
  erc-fill-mode: t
  erc-stamp-mode: t
  erc-netsplit-mode: t
  erc-irccontrols-mode: t
  erc-noncommands-mode: t
  erc-move-to-prompt-mode: t
  erc-readonly-mode: t
  display-time-mode: t
  shell-dirtrack-mode: t
  icomplete-mode: t
  show-paren-mode: t
  tooltip-mode: t
  global-eldoc-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  column-number-mode: t
  line-number-mode: t
  transient-mark-mode: t

Load-path shadows:
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/home/albinus/src/elpa/packages/debbugs/debbugs hides 
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/home/albinus/src/elpa/packages/debbugs/debbugs-pkg hides 
/home/albinus/.emacs.d/elpa/debbugs-0.11/debbugs-pkg
/home/albinus/src/elpa/packages/debbugs/debbugs-browse hides 
/home/albinus/.emacs.d/elpa/debbugs-0.11/debbugs-browse
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~/src/org-mode/lisp/org-archive hides 
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~/src/org-mode/lisp/org-footnote hides 
/usr/local/share/emacs/26.0.50/lisp/org/org-footnote
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~/src/org-mode/lisp/ob-ruby hides 
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~/src/org-mode/lisp/org-feed hides 
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Features:
(shadow warnings emacsbug time-stamp url-http-ntlm ntlm calc
calc-loaddefs calc-macs hmac-md5 hex-util md4 url-http url-gw url-queue
url-cache url url-proxy url-privacy url-expand url-methods url-history
url-cookie url-domsuf url-util shr svg dom browse-url flow-fill
mm-archive sort gnus-cite mail-extr gnus-bcklg gnus-async qp gnus-ml
pop3 utf-7 nndraft nnmh nnml network-stream nsm starttls gnus-agent
gnus-srvr gnus-score score-mode nnvirtual gnus-msg gnus-art mm-uu
mml2015 mm-view mml-smime smime dig mailcap gnus-cache gnus-sum nnnil
smtpmail sendmail gnus-demon nntp gnus-group gnus-undo gnus-start
gnus-cloud nnimap nnmail mail-source tls gnutls utf7 netrc nnoo
parse-time gnus-spec gnus-int gnus-range message puny rfc822 mml mml-sec
epa derived epg mm-decode mm-bodies mm-encode mail-parse rfc2231
mailabbrev gmm-utils mailheader gnus-win gnus nnheader subr-x gnus-util
rmail rmail-loaddefs rfc2047 rfc2045 ietf-drums mail-utils mm-util
mail-prsvr term/xterm xterm erc-notify erc-desktop-notifications
notifications dbus xml erc-list erc-menu erc-join erc-ring erc-networks
erc-pcomplete erc-track erc-match erc-button wid-edit erc-fill erc-stamp
erc-netsplit erc-goodies erc erc-backend erc-compat thingatpt pp
cperl-mode tramp-theme em-dirs esh-var esh-io esh-cmd esh-opt esh-ext
esh-proc esh-arg esh-groups eshell esh-module esh-mode esh-util
finder-inf docker-tramp tramp-cache slime-autoloads url-auth
vagrant-tramp dash term disp-table ehelp info package epg-config
url-handlers url-parse url-vars time tramp-sh tramp tramp-compat
tramp-loaddefs trampver ucs-normalize shell pcomplete comint ansi-color
ring format-spec advice auth-source cl-seq eieio eieio-core cl-macs
eieio-loaddefs password-cache ido seq byte-opt gv bytecomp byte-compile
cl-extra help-mode easymenu cconv jka-compr icomplete time-date paren
ps-print ps-print-loaddefs ps-def lpr vc cl-loaddefs pcase cl-lib
vc-dispatcher dired dired-loaddefs mule-util tooltip eldoc electric
uniquify ediff-hook vc-hooks lisp-float-type mwheel term/x-win x-win
term/common-win x-dnd tool-bar dnd fontset image regexp-opt fringe
tabulated-list newcomment elisp-mode lisp-mode prog-mode register page
menu-bar rfn-eshadow timer select scroll-bar mouse jit-lock font-lock
syntax facemenu font-core term/tty-colors frame cl-generic cham georgian
utf-8-lang misc-lang vietnamese tibetan thai tai-viet lao korean
japanese eucjp-ms cp51932 hebrew greek romanian slovak czech european
ethiopic indian cyrillic chinese charscript case-table epa-hook
jka-cmpr-hook help simple abbrev obarray minibuffer cl-preloaded nadvice
loaddefs button faces cus-face macroexp files text-properties overlay
sha1 md5 base64 format env code-pages mule custom widget
hashtable-print-readable backquote dbusbind inotify dynamic-setting
system-font-setting font-render-setting move-toolbar gtk x-toolkit x
multi-tty make-network-process emacs)

Memory information:
((conses 16 442924 56012)
 (symbols 48 42731 242)
 (miscs 40 64 385)
 (strings 32 95990 16664)
 (string-bytes 1 2905658)
 (vectors 16 58533)
 (vector-slots 8 958549 9259)
 (floats 8 715 711)
 (intervals 56 298 46)
 (buffers 976 21)
 (heap 1024 24409 155192))