Turn Off Rich Text Formatting in Exchange by Default!
By default, O365 Exchange is set to follow Outlook user settings for sending outgoing mail in RTF. This causes a LOT of issues with Apple iOS users and the native iOS email app not being able to read the RTF attachments. They only receive an unreadable Winmail.dat attachment which causes a LOT of headaches for MSP's like myself.
By default, PLEASE set the Exchange RTF format to "Never", otherwise, all Outlook settings throughout an organization will have to be checked and changed. RTF causes way too many issues and HTML formatting should be used, anyhow. And I'm not certain the default setting even works, even if the Outlook settings are changed.
Here is how the setting is changed manually:
From the Exchange admin center -> mail flow -> remote domains tab -> Edit the default domain -> Use rich-text format: Never -> Save