In the message view, you can open a popover for any sender or recipient account to see its linked identity. If the account is not yet linked to an identity, you can assign it to an existing identity (or create a new one) directly from that popover.

Open the message from your search results or message list. In the message, the sender and recipients are shown as clickable links (for example under the Sender, Recipients, From, or To labels, depending on platform).

Click the account (display name or address) to open its identity popover. If the account is already linked, the popover shows the identity card. If it is not linked, the popover shows "No linked identity" and the message "This account does not belong to an identity. Create a new identity for this account or assign it to an existing one."

In the popover, click Assign to identity. The Assign identity dialog opens, with the text "Assign [account] to an existing identity."

In the Identity field, start typing to search. Matching identities appear in the dropdown, each showing the person's name and primary email. Select the correct identity.

Click Assign identity. On success, an "Account assigned to identity" confirmation appears.

Note: If the account has no matching identity, you can instead click Create identity in the popover to create a new identity for it.