Send notification to previous Assignee when assignee changes on a Jira issue

Summary

When the assignee of a Jira issue is changed, the previous assignee doesn't get any notification that they no longer own that Jira issue.

Solution

Here are the steps to add an internal comment on a Jira issue when the assignee is changed mentioning the previous assignee. This will trigger the agent notification and notify them about the assignee change action: 

1. Go to Project Settings → Automation. Click on Create Rule.

2. Choose the Field Value Changed trigger and select the field Assignee for "Any changes to the field value" and for "All issue operations". Click Save.

3. On the next page, select Advanced Compare Condition. Use this condition to verify that the issue was assigned to another agent before the change: {{changelog.assignee.from}} does not equal empty. Click save.

4. Add a new action to Add Comment. Use the Smart Value [~accountid:{{changelog.assignee.from}}] to mention the previous assignee and add your message. Select the Comment Visibility as Internal Only. 

   When an assignee changes for an issue, an internal comment tagging the previous assignee will be added, triggering an email notification to the previous assignee about the change. 

5. Now, give your automation rule a name and 'Turn it on.'