Notification emails are sent using Sendgrid and they generally get delivered without any problems. However, occasionally they get stopped by spam filters and mimecast is often the cause. So if you are not receiving emails and you have checked the spam folder in your email app, then please contact your email administrators about whitelisting zokri.com and noreply@zokri.com.
For new users, you can send the invite link yourself - see How do I find the Invite link for a new user
If you are still having issues please contact support.
Minecast details
550 spamcop.mimecast.org Blocked - see https://community.mimecast.com/docs/DOC-1369#550