Problem:- System.EmailException: NO_MASS_MAIL_PERMISSION, Single email is not enabled for organization or profile.
Description : By default, email access level is set to “System Email only” or “No Access”. It allows only system generated email to be sent such as ‘Reset user password”.
Solution:- Following are the steps how to change email access level.
1. Go to Setup–>Email Administration–>Deliverability.
2. Set Email access level to “All Email” and then save the changes.