We've seen one user so far (perhaps others haven't noticed yet) with O365 sync issues using the native/apple mail client since updating to iOS 18.3.1. I'm quite certain it's an apple bug. We're Palo Alto firewalls and I show zero blocked traffic/url/threat from that source IP in our logs.  Yes using the Outlook app would be ideal and i'm sure Microsoft would prefer, but that's not something we can force on users yet. I'll reply back here if we make any progress. Lots of other rumblings on the internet about this issue. ... View more