If you don't receive the messages of HydroForum Group ; Go to : http://groups.yahoo.com/myprefs
then enter your Username & Password,
in the new page you will see your E-mail address,
at this time click on (Unbounce)
and then you will receive one E-mail in your Inbox with this subject :
Please reactivate your Yahoo! Groups account (Sender = Yahoo! Groups)
You should open this E-mail and click on the first link on that Mail
and then you will be able to receive the HydroForum messages.
If you do not receive the message within an hour, you can check the Bounce History for your E-mail address in : http://groups.yahoo.com/myprefs
and then click on Send Reactivation Request and follow the instructions.