It will be appended to the end of your mail. This configurations are editable using Setup panel and 'Save' button. This allows mail-merge tags to be replaced by their corresponding values depending on each entry. If not checked, mails are sent to all recipient list at once. Sent mails are marked so if an error occurs or you cancel the process you can resume where you stopped.
Press send button.
However, if you use custom or grouped method, MaxBulk Mailer take care of keeping track of sent mails for you so if you resume the process, no duplicate mail will be generated. You can check server responses with the log panel. Read 'About Maxbulk' document to find out how to register or upgrade to Pro version.