>I made a switch to Exchange Online for one of my accounts. In Outlook, I see, when using such account, we can no longer tell the server to remove emails once we read it. This is highly problematic as it keeps the same references on other devices such as in my iPhone. How can I tell Outlook to remove emails from Exchange Online server when I have read them in my inbox so they will not show in other inboxes, such as in my iPhone?

I don't know about the "delete after read" option, I didn't know about that and don't know anyone else who ever used it.

That said, with an Exchange account, all messages are on your Exchange server (in the cloud in your case). Everything you use to work with that account is just giving you a view (albeit with some local caching in some cases). If you delete a message in Outlook on a PC, it will soon disappear from your iPhone as well, since the iPhone is just giving you a view of what's in the cloud.

If the "delete after read" option is no longer available, you'll have to delete manually. If you're certain you'll never want to see a message again you can use Shift-Del to bypass the Deleted Items folder.