Currently, if the rule actor is different from the page author, the smart value {{page.author.emailAddress{}}} will return empty in the automation rule. The workaround is to change the page author's email visibility setting from Only you and admins to Anyone on Management Account page.

In Jira automation, there is a user called “Automation for Jira“ can be assigned as the default actor, which has access to all users' emails. It is better for Confluence Automation to support one similar actor.