Hi +Michael Keukert
Thank you for your response. The thing is... If I would send you an e-mail with any mail server available at the moment, adding an .ics attachment to it, the job is done. Clicking on the .ics attachment allows you to add the pre configured agenda item to your calendar. However, MailChimp doesn't allow to add attachments in its original format, but makes a link to it in their database.
Being able to add the agenda attachment itself would be a solution to the problem... But that's not possible then?