Thank you for your post.
Yes, "Send Mail" is available through Instant Web Publishing, but only through SMTP Server; not through the email client.
Pull down the Scripts menu and select "Manage Scripts...". Select the script that is causing the problem, or create a new script. At the bottom of the script steps, change the pop-up under Show compatibility to read "Web Publishing". Double-click on "Send Mail", and you will see on the right side:
Send Mail [ Send via E-mail Client (NOT COMPATIBLE) )
Therefore, you need to change the "Send via" from E-mail client to SMTP Server.
If you need clarification for any of the above steps, please let me know.