There are several reasons i think.
Before i use: "From:" Admin Email Address, with "Reply-To and i changed it to "From:" User Email Address (no "Reply-To:" field):.
I thougt THIS should had been the big issue. But not..
After poke around i figured out that i had upload a couple of components and moduls AND plugins just before this problem show up.
So first i made sure i hade an identically positions in all parameters regarding my PHP mail in Joomla and in Cb as my other site that worked.
I then unisntalled all the new components, moduls and plugin. And some more i might said when i was on the move..(or mood..)
Then it start working again.
The only problem now is (and i have ask this in another topic today). Is that when the conformation mail and the ok mail to a new members come to the members inbox in say yahoo.
It takes 30-60 minutes and it aslo goes in the spam mail inbox?
My other working site sends the mail directly witout delay.And don´t get in the spam inbox, it goes to the right "place" Your Mail inbox.
I can say that these to sites has diffrent hosts. Could that be the problem? Or can you set the time WHEN mail sending? And you avoid to NOT go in the spam box?