1. Either the email address is incorrect (please check in case there is a blank space in the email id or a special/accented character (e.g, é, â, î, ô, etc) used in the email id).

2.  Or the email ids might not have been created or approved by your IT team yet.

3. Or the email id is not activated by the user by the time you were trying to send the login details. 

4. Or the Engagedly's IP address has not been whitelisted by your IT Team (IP: 168.245.6.44, Sender Email: noreply@engagedly.com).

Please make sure that other emails are getting delivered to those users and then try to send the login invites.