Port25's testing service offers a tool to test email authentication, including SPF, DKIM, and Sender-ID. The tool allows users to send a test email to a special email address that will return a report on their authentication results and SpamAssassin score. The report provides detailed information about the tests, including the results of each check and any errors or warnings. This can be helpful for users who need to troubleshoot issues with their email authentication setup. Port25's testing service is highly regarded by the developer, who has used it for years and praises its support and features.