Hi Ron_A,
I understand after you upgraded to Office 365 after-upgrade for Enterprise, there are some problems with the emails sent to you. To troubleshoot the issue, I’d like to collect the following information:
1. Please help to capture some screenshots of the problematic emails both in Outlook Web App and Outlook client, so that I can understand the issue better.
2. Did this issue only happen to you or a lot of users in your organization?
3. Did the same problem occur when you send emails to others directly?
4. Did this issue happen to the emails sent from specific users or many users, such as internal users and external users?
5. Are there any problems with the existed emails in your inbox?
Meanwhile, to eliminate network issue, you can try accessing your Outlook Web App on other computers outside your organization to see if the same issue will happen.
Thanks,
Vivian Wang