GMailSend Address Checker is a Chrome add-on developed by SEYA.WORK. It is a free tool designed to prevent accidental email sending by checking the From, To, Cc, Bcc, subject, and attachments before sending an email.

The add-on modifies the "Send" button in Gmail to a "Confirm" button. When the user clicks the "Confirm" button, a confirmation dialog opens, allowing them to review all the fields mentioned above. Once they have reviewed and confirmed the details, they can click "OK" to close the dialog and proceed with sending the email.

One notable feature of GMailSend Address Checker is that it highlights any recipient addresses that do not match the sender's domain in red, helping users to identify potential mistakes. The add-on also supports multiple languages, including English, Chinese (Traditional and Simplified), Korean, Vietnamese, and German.

Overall, GMailSend Address Checker is a useful tool for Gmail users who want to avoid accidental email sending and ensure the accuracy of their email details.