Hello, @Damian Teasdale,
Welcome to the Microsoft Q&A platform!
Based on your description, I understand that your Teams status for external contacts does not show up in Outlook, even though it shows up properly for internal contacts.
I can understand your needs, but unfortunately, as is shown in the screenshot below, Outlook currently shows Status unknown for federated (external) Teams contacts, so you can't check their status directly when you send an email on Outlook, you can only check their status by clicking on the external contact.
For more information, please refer to this document:https://learn.microsoft.com/en-us/microsoftteams/troubleshoot/teams-im-presence/issues-with-presence-in-outlook?tabs=64#known-issues.
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Thank you for your support and understanding.
Best Wishes,
Alex Zhang