Exact same symptoms here too.
1 - started after Exchange 2019 CU14
2 - only appearing on emails sent from internal email accounts
3 - yellow envelope appearing, no additional information when hovering mouse over icon
4 - yellow envelope changes to reply/forward arrow depending on action.
5 - affecting outlook 2019, 2021 H&B versions so far.
6 - does not affect OWA - no envelope appearing
Could we have clarification if this is a new feature, and what it means, as it is not evident?
Or, can you let us know that it is in fact a small bug and will there be a new update to fix?
Thank You