Dear Stuart Garett
Good day!
Thank you for posting in Microsoft Community. We are happy to help!
Per your description I understand you would like to change the default paragraph spacing, after testing , I found that this may not be directly achieved in the manner you want, however since your Team mates will apply this method it will work with only mail they send and mail sent from non -team members will not have the same spacing set.

Then select line and paragraph spacing > spacing options
Then in the window that appears set the spacing to before 6pt and after 0pt, then select set as default


Please feel free to let me know how it goes. Looking forward to your reply.
Sincerely,
Momo | Microsoft Community Moderator
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