The email is detected successfully by the trigger, but the category assignment action cannot locate or process the mailbox item and returns ErrorInvalidMailboxItemId.

Question

The email is detected successfully by the trigger, but the category assignment action cannot locate or process the mailbox item and returns ErrorInvalidMailboxItemId.

Solsvik, Kjersti 20

Questions for Microsoft

Under what conditions does the Outlook connector return ErrorInvalidMailboxItemId when assigning categories to emails in a shared mailbox?

Does the Assign Outlook Category action require a specific mailbox parameter when used with the When a new email arrives in a shared mailbox trigger?

Are there known issues or limitations when passing the trigger's Message Id to the category assignment action in shared mailboxes?

Are there connector version or configuration requirements for categorizing emails in shared mailboxes?

Solsvik, Kjersti 20 Reputation points

2026-08-20T12:03:35.2166667+00:00

Internal IT team believes the issue may be related to Outlook connector behavior rather than environment configuration.

Answer accepted by question author

0 additional answers

Your answer

Solsvik, Kjersti 20 Reputation points

2026-08-20T12:03:35.2166667+00:00

Internal IT team believes the issue may be related to Outlook connector behavior rather than environment configuration.

Answer 1

Hello @Solsvik, Kjersti,

Good day! I hope you're doing well.

Based on your description, this issue appears to be related to the behavior of the Power Automate Outlook connector when working with shared mailboxes, specifically the "Assign Outlook Category" action and the ErrorInvalidMailboxItemId error. The available information suggests this is more closely associated with Power Automate connector functionality and shared mailbox handling than with Outlook on the web or general Microsoft 365 configuration.

To ensure you receive accurate, up-to-date, and technically specialized assistance, I recommend posting your question in the Microsoft Power Platform Community Forum: Microsoft Power Platform Community Forum Thread

User's image

This forum is dedicated to Power Automate and other Power Platform technologies, and it is actively monitored by Microsoft engineers, MVPs, and Power Platform experts who are familiar with connector limitations, shared mailbox scenarios, and known product issues. You are more likely to receive confirmed guidance, workarounds, or information regarding any known limitations of the Outlook connector.

The reason for this redirection is that troubleshooting Power Automate flow actions, connector behavior, and automation-specific errors falls within the Power Platform scope. Since this issue appears to involve the interaction between a shared mailbox trigger and the Assign Outlook Category action, the Power Platform Community is the most appropriate venue for further investigation.

I sincerely apologize for any inconvenience this redirection may cause. My goal is to help you reach the support channel best equipped to investigate and address this issue, and in this case, the Power Platform Community is likely to provide the most relevant assistance.

Thank you for your understanding. Have a nice day and stay healthy!

Note: Please follow the steps in the forum documentation to enable e-mail notifications if you want to receive the related email notification for this thread.

Solsvik, Kjersti 20 Reputation points

2026-08-21T08:46:49.74+00:00

Thanks for you quick answer, this was very helpful.
Roebe Ta 865 Reputation points Independent Advisor

2026-08-21T11:54:35.93+00:00

Thanks for your kind response. I hope your issue will be resolved soon!