GMailSend Address Checker is a Firefox extension designed to enhance the email sending process by providing a confirmation dialog before sending emails. This tool is particularly useful for preventing errors by allowing users to verify recipient addresses and subject lines before finalizing the send action. The extension modifies the Gmail interface by replacing the standard 'Send' button with a 'Confirm' button, which triggers a dialog that displays all relevant email details including From, To, Cc, Bcc, Subject, and Attachments. Users must confirm these details to proceed with sending the email, thus minimizing the risk of mistakes.

In addition to its primary functionality, GMailSend Address Checker includes features such as highlighting email addresses that do not match the sender's domain in red for easy identification. The extension supports multiple languages, including English, Chinese, Korean, Vietnamese, and German, making it accessible to a wide range of users. Recent updates have added compatibility with 'Mailtrack for Gmail' and introduced a donation button for COVID-19 medical support, highlighting its commitment to user needs and community support.