which CMS will allow me to work offline. I want to teach my students even though there is no connection (I live in Africa and once there is power outage):I want to receive their message, I want to post messages, etc..
i love drupal there is a module to to enable offline
I am not a Drupal expert however, I have some non-drupal ideas.. first, I want to make sure I understand what you want to do...
You want to be able to access a CMS, along with your students even when internet access is not available?
#1 To totally by-pass the internet and just work offline without any internet connection, you would need to do a 'local' installation of drupal on a computer you will network internally This link could help with that http://drupal.org/node/238805 . (I'm also not a network person...but I have used the Moodle LMS in a networked offline setting).
I don't think you're after the solution above, though so I'll offer another idea that deals more with an intermittent internet connection - sometimes it's on and sometimes off.
#2 Do you need a content management system that allows you to download needed content when you're connected to the internet, then, when you're not connected you can read/write emails and have them sitting in a cue ready to send themselves the next time the computer is connected?
If #2, above, is what you're after...I don't know of a drupal or even Moodle module that does that - it would be great if there is one...really helpful for so many people connecting to the internet through less than ideal setups!
One idea, I have for you is more of a low-tech content management system using shared files through 'drop-box'. DropBox can be useful in that you can upload, share files across many different computers - when the computer is connected it syncs to the dropbox, downloading and uploading files as necessary. Here's a blog posting that talks about using DropBox in schools and another one about how to get free storage space.
I also found a dropbox module for Drupal so that may help you. And here is a link to an opensource dropbox-like project called ifolder which may have Drupal possibilities.
If you decide to use dropbox, this article might give you some ideas on how it can be tweaked to meet your needs. In particular, you can learn how to download something to your dropbox when you're not online - which might save you lots of time/money since you can download large files to your dropbox when you're offline and then download to from your dropbox when you're on a fast connection.
Other dropbox-like products you may want to check: windows live sync, unison.
I think I understand what you're looking for so I hope these suggestions might help.