If you are looking for fast method to post maintenance mode message on your wordpress blog than you must try Wartungsmodus wordpress Plugin . This Plugin helps you to add a maintenance mode message page on your blog that lets visitors know your blog is down for maintenance time .
View full review and information here
There's another similar plugin that's just called "maintenance mode." It allows customization but it gets in the way of accessing the feed. Does this one do that also? I know that people sometimes put up "subscribe to the feed" links on maintenance pages, but it does no good if the feed is broken.
I have not tried it for too long but you can ask questions to developer of this plugin here - WP – !Wartungsmodus (Plugin) – bueltge.de [by:ltge.de]
Great plugin, better than the other one who just shows a blank page with blue letters
Thanks for sharing!