Using Classic Outlook on Windows for personal email, calendar, and contact management
Hello Ramesh,
Good day! Thank you for posting to Micrsoft community.
To answer your query, I'm afraid Outlook does not support border radius. This is because Outlook uses Microsoft Word as its rendering engine, which does not support this feature. We apologize if we are not able to meet your requirements. However, we will surely raise you concerns to our Product Team and hopefully this can be included in the future updates.
In the meantime, I did find similar post in the feedback forum Support Border-radius in emails · Community (microsoft.com). You can upvote or add a comment to push for this if it is in line with your requirement. Otherwise, you can as well raise a new entry in the forum on link Outlook · Community (microsoft.com) such that it can be considered for development by the product team. Many features are designed and upgraded based on customers’ feedback.
I will also update here once I get any update on this feature. Thank you for your kind understanding.
Best Regards,
Ashraf.