@Nutan Kumari You can try exploring the Notifications and email templates in Azure API Management if this is something that can help with your business requirement which trigger when a specific event occurred.
If in general, you want to send emails to all your user then you need to build your own solution. You can leverage the Get all User for APIM Instance PowerShell command that returns all user and their properties. Now you can iterate through the result set to get only the email IDs or as per your requirement. Once you have the list of user email IDs you can further automate it using the Send-MailMessage command. This workflow is only for reference and you can leverage the Management REST, etc in whichever way you are comfortable with.