Disappearing emails on iPhone 15 Pro with 365 setup

Hello,

has anyone ever solved this question where send an email from the IOS native mail app using 365 setup and it just vanishes into thin air?

have tried turning send delay off

deleted the mail account, restarted device and added the account again

always been on the latest iOS version

expensive phones for such a simple task to be done? Im at a total loss on what to try next .

iPhone is a 15 pro as-well, plenty of storage

[Re-Titled by Moderator]