Registration Emails sent from Easysocial should use Joomla SMTP Mail Setting

I don't know how the registration e-mails are send from EasySocial to final users waiting for the precious activation link, but i've noticed something :

A. My users can register via Slogin who seems to use Joomla SMTP settings (in my case i use Mailjet). 100% of my new users who signed in using Slogin are not blocked (are enabled) and has clicked on the activation link (are activated).

B. Since i use Joomla SMTP settings and Mailjet for Acymailing, 100% of my newsletter subscribers received the link to confrm their subscription.

C. I know when my users has registered on my site using Easysocial (because they have a profile type). In this case, about 40% of my users using Easysocial registration process are not enabled and never activate their account ! It's a lot ! It seems they never received the activation link from EasySocial...

My question is, could Easysocial use Joomla SMTP settings or Mailjet API settings to send activation links ? Or maybe have i an issue somewhere...