Hi @ragau,
Welcome to Microsoft Q&A, and thank you very much for reaching out to us.
Based on your description, may I verify that you would like to disable the Mail Tip when sending email to external recipient?
If that is the case, aside from using Exchange Online PowerShell method, you can also check the Microsoft Defender Portal, provided you have the necessary admin permissions. Specifically, look at whether your Anti‑phishing policy has the “First contact safety tip” feature enabled. When this feature is on, Outlook may display warning banners that can look similar to MailTips.
Go to M365 Defender>Email & Collaboration> Policies & rules > Threat Policies> Anti-phishing, edit policy and switch off first contact safety tip.
For more information, you can check this Microsoft documentation here.
I hope this helps. Looking forward to your response.
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.