Thanks for your post.
Both the Send Mail function and the creation of new accounts are both possible only via the FileMaker Pro or Pro Advanced programs themselves. The browser does not have the capabilities to directly trigger a mail send, though you can always copy and paste any email data from the database into an email you wish to send manually. The browser also cannot make structural changes to the database, which is where you would add or modify user accounts.
These are limitations of the browser functionality.