Transactional emails are, in fact, a part of application’s UI. In practice, it may be most problematic, because emails can be non-delivered, can be delivered to SPAM folder, can fail to display correctly in some specific application or become unreadable. Unlike web testing, which is well documented in thousands of books and articles, emails often are lost on testers, and this leads to troubles. The talk explains how and when the mail components, like a mail infrastructure, generating scripts and applications, templates and mail data should be tested. It also points to most problematic places and key points for testing. The talk may be used for both managers who plan the application testing in general and specialists responsible for test development and testing of mail components.