This is due to the fact that cloud version of Jira does not provide apps with access to its mail queue. This is unlike server version of Jira where apps send emails via Jira's mail queue. Using your own email address can be desirable for a number of reasons, such as corporate firewalls & need for personalisation etc.
It is possible to configure an email address from your own domain & use it to send emails generated by ARN.
Set up credentials
Jira administrators will be able to see the 'Configurations' page under Settings → Apps → Automated Release Notes section.
Choose the service provider - currently Gmail, Outlook, Office365, Sendgrid, Mailgun are supported. Provide email & password before clicking on 'Submit'. If service provider along with credentials match, a success message will be displayed & this config will be available from within the rules.
Use your own provider
You can even choose ‘Other’ option from the dropdown. It lets you add your own configurations - right from the SMTP host & port to your email & password.
Our recommendation is - create a non-user email address specifically for release notes & use those credentials here.
These credentials are stored in database. They are encrypted & can be decrypted only by the application.