Mass mail works well but nobody gets his mail

I've configured joomla with phpmail
when I sent a mass mail, interface tells me
"Sent email to 5 of 5 users"
no errors but nobody gets the message.
Is there something else to do in configuration in order to users get really a mail in their inbox or spambox?
My users are registered with community builder (CB)login ? Is there something to configure in this side ?
Remark: mass mailing with joomla "kernel" provides a similar error
But I don't know if mass mailing doesn't work because there is a missing parameter in joomla configuration or it's because users are registered in CB and I have to configure something at this level
Thanks in advance for reply

CB has nothing to do with this.

If your Joomla mass emailing doesn't work then no other emailing will work on your website.