I would like to send a message to a user on a certain time if this user 
is online and if he is not online send him an email. Is this possible? 
Because untill know I only see how to do things responding to a request.

There are various timer options on the server such as the AT command or a 
CRON job that you can arrange to run at a certain time.

At 15:27 12/05/02 +0000, you wrote:
>I would like to send a message to a user on a certain time if this user
>is online and if he is not online send him an email. Is this possible?
>Because untill know I only see how to do things responding to a request.
>
>---
>
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