user hotmail not receiving registration email

Hello there, I have a strange issue.

It seems that user from hotmail and probably gmail don't receive the registration emails.

I even switched from phpmail to smtp .. but nothing ...

I did some test and the strange thing is the email can receive email from our email address but cannot receive from the registration.

It is like they erase the email or the never arrive ...I am a bit lost.

In case to make sure ... where is located the email that make start and send the registration and what service easysocial use to send email?

Best Regards
Antonio