In my case i’ve found that mails were sent but classified as spam.
Unfortunatelly some mail servers are blacklisted by some ISP for spamming reasons.
I’m looking for solve this problem because people that want to register in my site are unable to receive properly the activation code sent by email.
For now i change the output message shown in the registration process, alerting people to check into the spam folder, but hope to solve it in a better way