Kesavan, the Send Mail script step has this in the Help topic:
Perform without dialog instructs FileMaker Pro to put the composed email message in the email application's outbox, ready to be sent. If this option is not selected, the composed message is left open in the email application so it can be reviewed. In Microsoft Outlook Express or Microsoft Entourage on the Macintosh operating system, the new message is left in the Drafts folder.
Do you have the checkbox "Perform without dialog" checked or not? and does it make a difference?
TIP: I will have my computer off network (wifi, ethernet, etc.) while testing these kinds of things. No mail can go out that way. You can then delete them before going back on network. But if you are working on the Hosted files (with FileMaker Server), then you can't do this!