Lounge

I'm no Moodle expert, but to accomplish the task you have stated...

"You are adding a new topic for a lesson and you want to inform the students whre are subscribed in this lesson for this new thread by emailing them."

Assuming the course is limited to only the current students enrolled, then , on the main paige of your course, go to the People Block, click on Participants... This will list all the students in the course.

Next, click on select all, located at the bottom of the page. This will place a check mark in all the boxes to the right of each participants name. Next, click on the Selected Users drop down box and choose send a message, Create your message in the next screen that appears, click preview and then click send message.

This will send a message to everyone in your course, and forward an email to them if they are not online depending on their setup.

I don't know what php mail is, but the method I describe works really well for contacting all students with one message from the instructor. It is basically utilizing the messaging system in moodle with the email forwarding option.

Hope this is helpful, at least until you figure out an alternative.

Linda