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outlook - shared mailbox signature - signature to match the "From:" mailbox - create flow

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Posted on by NK-18061413-0

Outlook online and desktop does not allow the user to allocate a default signature for a shared mailbox delegated to the user.

Outlook on Android allows this (so it's not a licencing/MS Exchange issue).

I have raised a ticket with the Outlook team and I was promised that developers will look into it. Until this is fixed (if at all) I need a Power Automate flow to do this. The Customer Support team (on two separate tickets I raised) could not help me and directed me here or to commercial Partners. I shouldn't have to pay for fixing a functionality flaw in M365.

The trigger is the user selecting a shared mailbox (when composing new email/replying) and the action is selecting a particular signature to attach in the message from the drop-down menu.

Could someone help? I have never used power automate.

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Building flows

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David_MA 14,278 Super User 2026 Season 1 on at

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Please show the configuration of your trigger action. I don't understand how a flow can trigger with a shared mailbox and the user can choose what mailbox it triggers on. Are you referring to this trigger:

If so, you can only choose one shared mailbox.

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WillPage 2,329 Super User 2026 Season 1 on at

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You can get around this by signing into the shared mailbox with a username and password as if it were a user mailbox. The shared mailbox will appear in the Users list in the M365 admin centre where you can reset the password. You can temporarily assign a license if you want to stay on the right side of every MS licensing T&C. Then you can sign in with Outlook Online like it's a normal user mailbox, set the signature then afterwards revert it back to a shared mailbox.

If this doesn't work or it's just too hard dealing with your IT department, then consider using this technique to add an inline image into the signature block in Power Automate: https://willpage.dev/2024/01/08/sending-emails-with-inline-attachments-in-power-automate-logic-apps/

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