FYI – just had our IT team look at this. When sending to Outlook365 emails, the formatting CSS doesn’t remain; it strips. When sending to Gmail, iCloud, etc., it works. It appears that the new update is stripping the formatting/style coding when sending to Office365 email addresses.
Not sure if it’s all Microsoft (hotmail, MSN, outlook.com, etc.), but we do know it’s Outlook365 emails for sure (not just our org).