Hopefully my final edit... @Anonymous alerted us that Microsoft has added a "Mailbox Address" field to Outlook actions. You can enter the address of the shared mailbox in this field to get back to original functionality. I'm keeping all previous solution details below just in case.
I've accepted the solution provided by @Anonymous on page 3. As a note for future users running into this issue, this solution requires a premium account. This will not be the best solution for a number of users (myself included), but it's the Microsoft-supported fix and (hopefully) the least likely to fail in the future.
For more information on the Graph API solution, check the posts by @jonathanford on pages 5 and 6.
If you do not have a premium account, the solution on page 3 offered by @Mindaugas is your best bet. You will need to add a new connection to Flow for the shared mailbox and then select that account as the connection for your Flow step. @RHCC gives more details on page 4 - you will also most likely need to add a password to the shared mailbox which is not intuitive.
This is by far the easiest solution, but I'm concerned how long it will work before Microsoft breaks functionality in an update. They do not support shared mailbox connections in Flows that don't specifically use that language, which is a frustrating response given how many users were relying on these Flows for their daily business.
Original post below:
Hi all - I'm having an issue with a couple Flows that were previously working without error.
When a new email arrives in a shared mailbox runs in a separate Flow and creates a SharePoint list item. One of the attributes added is the id of the trigger email (MessageId from the triggerBody).
I have two other Flows that will reply to this initial email using Reply to email. The stored MessageId is used to reply to the correct email. This has been working for 4+ months without error, but started failing today with the error shown in the Subject (Item Id doesn't belong to the current mailbox).
Myself and one other user are not having this failure. I had a user who was experiencing the failure check their connections in Flow and all apps were still connected. I also had them check their access to the shared inbox in Outlook and they still had full access.
Has anyone run into something similar or have any suggestions? It seems like it must be a user connection to the shared inbox but I'm not sure what else to look into. Thanks!
**Editing to note that the Get email step is also failing when referencing the ID of an email in a shared mailbox.
