Activation email not sent

Hello, I use the 1.7 version of Community Builder in Joomla 1.5.23, but I encounter a problem that can not find solution. When a user performs its registration, the system does not send the email to confirm registration. I performed several tests and found that only emails are not arriving to the Terra and Bol.

Could you help me with this problem.

thanks

the problem is not CB is your mail server. it might be blacklisted on those providers.
check for a returning email and contact them.