The default mail handlers that come with Jira are often enough for simple email processing needs. If you need to have more control or need special processing logic for your incoming emails, you can create custom mail handlers. However, creating new mail handlers requires you to have knowledge of programming; a better option is to use an add-on called Enterprise Email Handler for Jira (JEMH).

With JEMH, you can set up advanced email routing, additional email triggered operations such as updating an issue based on your email content, an audit of received/processed emails, and more. You can find out more about JEMH at https://marketplace.atlassian.com/apps/4832/enterprise-email-handler-for-jira-jemh.