Add option to reply to invitation mails by plain email

[loibpet]

Is your feature request related to a problem? Please describe.

Protected networks have no access from the internet and are accessible from internal networks only. This is usually done to protect potentially sensitive information or reduce a possible attack vector and is quite common in many organziations. Access to these networks is usually done with VPN tunnels or the WebRas. This has the effect, that such a nextcloud installation is not accessible from the internet. In many cases, not even the FQDN is resolvable from the internet.

However, this has implications if a calendar invitation is sent to an external party as the "accept" or "deny" of such an invitation will try to access the FQDN for the nextcloud installation. However, this is not possible from outside the orginistation.

Describe the solution you'd like

It would be more than helpful, if there would be a configuration switch for the administrators that allow to toggle between the current behaviour for invitations, and the possibility to reply to such an invitation by plain email (e.g. as described in RFC 5546). An example for such invitations would be Outlook or Thunderbird.

Describe alternatives you've considered

Not using Nextcloud

[Beeez]

If the external user who is accepting a calendar invitation, how else would nextcloud possibly get notified of the accepted invitation?

The only possible way is to have some kind of endpoint that can be integrated that acts as a middle man, but that would probably require hosting of a service from nextcloud similar to their mobile push notification endpoints.

[loibpet]

Pls. check issue #5080. Once this is done, then the invitation will contain the individual email of the owner of the invitation. Any response to such an invitation will then be sent back to the mail address of the owner and not to the generic one. This way, the calendar app is able to process any feedback.

[miaulalala]

Not iTIP neccessarily, but we're working on iMIP at the moment (RFC6047).

[satyamkapoor]

Not iTIP neccessarily, but we're working on iMIP at the moment (RFC6047).

Let us know if you need any help in implementation. This feature is kind of super important for making calendar usable professionally.

Till we have a solution, I found if one uses Thunderbird, the event reply mail is processed by the client which updates the main event in Thunderbird calendar. Too much dependency on thunderbird in this case ;'(

[miaulalala]

Not iTIP neccessarily, but we're working on iMIP at the moment (RFC6047).

Let us know if you need any help in implementation. This feature is kind of super important for making calendar usable professionally.

Till we have a solution, I found if one uses Thunderbird, the event reply mail is processed by the client which updates the main event in Thunderbird calendar. Too much dependency on thunderbird in this case ;'(

if you're knowledgeable about Calendaring and Scheduling (plus PHP), I would love your input on #33001 if you have time!

There's three more parts that are done in the mail app - the processing of invitations is triggered from there, plus the analysis and display of pertinent scheduling information and buttons.