Meeting invitations to configured aliases are not treated properly

[tom-ch1]

Steps to reproduce

1. configure email system so that main@example.com and alt@example.com arrive at the same mailbox
2. add an account for main@example.com in nextcloud mail
3. configure an alias alt@example.com to your main@example.com account
4. send a meeting invitation from outlook to alt@example.com

Expected behavior

The meeting invitation should be treated in the same way as if it were sent to main@example.com:

• there should be options to accept, decline etc.
• the invitation should be added to the calendar if accepted

Actual behavior

The meeting invitation is recognised as such, but:

• the following message is displayed: This message has an attached invitation but the invitation does not contain a participant that matches any configured mail account address
• There is not way to accept, decline etc. and no way to add the meeting to the calendar

Mail app version

5.1.6

Nextcloud version

31.0.4

Mailserver or service

local mailserver (exim and dovecot)

Operating system

debian

PHP engine version

PHP 8.2

Nextcloud memory caching

No response

Web server

Apache (supported)

Database

PostgreSQL

Additional info

No response

[kesselb]

Thanks for the issue 👍

We are aware that the current implementation, which shows the iMIP options only when the recipient matches, isn't ideal and leads to confusion. I guess it makes sense, similar to Thunderbird, to refine the logic and, if we are unable to find the right calendar, ask the user for it.

Related: #10788

[st3iny]

The CalDAV backend not handles aliases correctly when processing iMip messages.

However, the Mail app still does not recognize them and will show an incorrect iMip box. The confusing warning message is still shown.

Workaround: Import the event into the calendar manually. Changes via iMip will then be processed correctly.

Note: The fix is only available on Nextcloud 32 so far. The backport to 31 is still pending.

cc @SebastianKrupinski

[SebastianKrupinski]

As per #11915 (comment) this should be fixed now