After here is a description for the past v1.x series.
Check the message contents and addresses before you send the message.
You can check the followings:
(1) whether the words you pre-defined exist in the message and the message does not have any attachments,
(2) whether the words you pre-defined exist in the message,
(3) whether the recipients exist or do not exist in the address books.
Finally it confirm you are ready to send message.
Each checking is enabled/disabled by Check and Send's option. Don't forget setup the checking before you use this extension.