iOS Mail App no Push / ActiveSync

[vele]

You are on IMAP not on Active Sync as per your screenshot.
Push does work on Active Sync but sending via Active Sync does not.

Delete your account from your Iphone and try again. Setup Microsoft exchange (find your server address usually box.yourdomain.com in the MIAB Admin panel Instructions):
Set up Exchange ActiveSync on your iPhone, iPad, or Apple Vision Pro - Apple Support (MK)

Read more:

[Solved] Autoconfiguration not working for iOS / Z-Push Support

Normally that is the message when accessing /Microsoft-Server-ActiveSync through the browser and not a phones mail client. Is this what you are getting when using your phone? This is saying that the user/device hasn’t been provisioned yet. If you remove the account from the phone and then re add it does it start working?