How to send Calendar entry to Notes from external source?

I want that mail to include information which Notes will consider as Calendar Entry, so that the person who receives this mail will press a button, and add this entry to his personal calendar. - just as a regular native notes meeting invitation.

If the person decides to decline or accept the meeting, Notes will receive mail to the sender.

I know that it is possible to send meeting invitation from Outlook to Notes, and Notes recognise those mails as calendar entries.

Where can I find a source for creating such a mail.

The “External Source” I want to use is an SMTP mail, from a web application (e.g ASP CDONTS).

Any ides?