Hi @Admin User (v) ,
Welcome to our forum!
How can I customize the ribbon in Outlook on the web (OWA) for all domain users via group policy to increase the visibility of my add-in and ensure that the changes are reflected for all users?
I'm afraid that we cannot use group policy to make the change for all user's OWA.
As i know, we can try the following articles to make some uniform changes for all domain users, but not include your reauirement:
Create a mailbox policy in Exchange Online for Outlook on the web and the new Outlook for Windows
Customize the Outlook on the web sign-in, language selection, and error pages in Exchange Server
Please kindly understand that many functions are not designed at present. It is recommended that you could post the functions you expect and your sincere suggestions on the website dedicated to collecting feedback. We sincerely welcome your suggestions, and thanks for your understanding and support!
If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
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.