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I want to programmatically send iCalendar invitations via Email. The relevant standard for that seems to be iMIP. RFC 6047 shows in section 2.5 an example where the iCalendar is sent as the sole content of the mail. In section 4.2 there is an example where a plain text alternative is added. I implemented that in my application and it works well with my limited test scenarios.

However there is advice that the iCalendar message should additionally be added as an attachment. Examples for that advice are

  1. https://devguide.calconnect.org/iMIP/iMIPBest-Practices
  2. Multipart email with text and calendar: Outlook doesn't recognize ics

I find this a bit dubious as the media type application/ics is not registered with IANA.

So, my question is: Are there really still clients that require the invitation as attachment? Or is this a case of cargo cult programming?

I searched for a explanation why the invitation should be included twice in the Email. But I only found the general advice to include it. Gmail and Thunderbird do add the attachment when sending an invitation. But SOGo does not.

BarneySchmale
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  • According to https://stackoverflow.com/questions/19523861/multipart-email-with-text-and-calendar-outlook-doesnt-recognize-ics there were issues where Outlook 2007 had an issue with 'text/calendar' embedded in a 'multipart/alternative'. But is this still an issue? – BarneySchmale Mar 25 '23 at 10:43

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