subscribe by email don't send email confirmation to subscribers

I think we had this before but I can't find the old thread.
I am trying to subscribe to the following subsite but the plugin SBE don't send an email to confirm the subscribtion.
Last time I remember that there was a conflict with Subscribtion from Jetpack.
So this time Subscribtion is not active but still SBE is not sending out an email.
Can you help?
Support access is granted as well.