Gitlab CE, password reset email not sent when creating users from admin area

Hi, I have gitlab ce running on GCP instance. Everything is running fine. I have sign up disabled and I am trying to add users from admin area. I have entered corrected email address and the email of the users show as verified. But the users say that they have not received any email. I tried with my own spare email and the invitation has not arrived? What could be the issues? Do I need to configure any email server on the instance? Is there anything I am missing?