This feature is not something currently supported by Front, but has been requested in the Front Roadmap section and has 156 upvotes so far. You can leave a comment on it or upvote it if you would like.

I can’t seem to find a share link but you can search the Roadmap for “importance” to find it.

I wanted to let you know that the feature you're requesting is an Outlook-specific feature.

Our research found that an email flagged as urgent or high importance in Outlook only shows up as urgent or high importance to the recipient if they are also using Outlook or Thunderbird. Recipients using Gmail or Front, etc., do not see this distinction. Because of this, Front has decided not to build this feature at this time.

That said, your feedback is very important to us. Please continue to share your feature requests with us! Our Product Team tracks feedback carefully and prioritizes building new features based on how many teams have requested them.

Please let us know if you have any questions or if there's anything we can do to help further!