Email and answer to a discution

I add that when someone responds to a discussion, the mail sent to inform that a response has been made is not received every time ...
I set in the back end sending mail when an answer is posted. Is there another setting to receive all the answers ?

ChronoForum V1

No body can help me ?
I really don't understand why somme mail are received and others no...
a bad setting? a wrong use ? an bug ?
Thanks for your help.
Fred

Maybe I did not understand the rules of notification?
For me, all the people who posted a message received autiomatically an email, during the answers.
Outside, I realize that only the last person who answered receives the notification email ...
Can someone remind me of the notification rules? is there a document?