New Outlook won't let me add my outlook email account.

I don't know about @L Tate -- but I do have aliases. Quite a few, actually. Most notably, while I use my main personal email (self-hosted) to login pretty much everywhere that is Microsoft-related (even LinkedIn and GitHub!), the original email address for Outlook.com (created eons ago) has absolutely nothing to do with anything else. It's just the word outlook_ followed by a random sequence of letters (possibly an ancient, pre-historic user ID -- I have no way of knowing).

The "old" Outlook, as well as Outlook.com, and Microsoft Exchange before that, never had the slightest issue with that. It's simply something that I consider "legacy".

I can imagine that the main issues with the "New Outlook" comes from fairly old Outlook.com users, who might have signed up during the Hotmail era (/me points to self) and have gone from migration to migration, eventually bumping into a wall with the New Outlook.

Generally speaking, the New Outlook struggles with those cases where the email address is not the login. While the former is pretty much standard these days, in the past, and not that distant past, one thing was your mailbox account, the other thing was your email address -- of which you could have many (aliases). There wasn't a clear-cut concept of "primary" email address and "secondary" or "alias" email address(es). These were just... email addresses. And then you had your login/password for your mailbox. Simple.

For well over a decade or so, however, mailbox providers (not only Microsoft, of course) have moved to the concept that the "main" email address is the login username. This makes sense, because, the way email works, all email addresses must be unique world-wide and tied to a specific user forever. As such, they are prime candidates for becoming usernames. Nothing wrong with that approach, of course.

The problem, AFAICS, is that so-called "legacy users" progressively migrated from having a login/password combination to unlock their mailbox to the contemporary usage of having their email address as a replacement for their "old" login.

In general, these progressive migrations have worked out without many hiccups. It's just that one day you still used the login/password method, and on the next day, you started using your brand new "Microsoft Account ID" to log in instead (which could actually use a different address, unrelated to your old Hotmail address). And, at some point, the migration was complete; the old login/password method ceased to exist; instead, you used your Microsoft Account ID to essentially connect to everything that is Microsoft-related. There isn't even a choice for "reverting" the process, since, technically, the legacy login/password don't even exist in their systems any more (I even forgot them by now; likewise with OneDrive, which was bought by Microsoft when it was still called SkyDrive, and those accounts were also migrated to the new system).

That doesn't mean that your ancient, legacy mailbox from Jurassic times disappeared. It's still there (no emails ever lost!). There is an internal mechanism to connect whatever email addresses you have registered with Microsoft to that mailbox. And the mailbox has its own ID, which only matters for the Microsoft DevOps team -- we, end-users, cannot do anything with it. We cannot even change it in any way. Even our awareness that such a "mailbox id" exists is being progressively phased out. The "old" Outlook still knows about its existence, though, and still displays it, although there is nothing you can do with it (I believe that you cannot even receive any email there). Clearly, to sort out the mess, Microsoft is keen in getting everybody to switch over to the New Outlook, where such legacy details are cleverly hidden to the end-user. Which I believe to be a Good Thing! It's pointless to show end-users information that they cannot use for anything (it's just confusing!), so I welcome the change.

But at the very very very least, New Outlook must consider the possibility that mailbox providers may not use the entire email address as a valid login for their services. This is a flawed assumption -- just because it holds true for Microsoft, Gmail, and Yahoo (at least!), it is not a "universal requirement". And it's possible that in the corporate world (where Microsoft rules supreme) such "guidelines" are not respected.

So... I appreciate the change to New Outlook in 2024, sure... but I hope Microsoft fixes this "legacy" issue. At least on Windows -- I'm currently on a Mac, and I'm well aware that whatever Microsoft fixes on Windows first may take a while to reach the Mac as well (I had to stop using my Microsoft email address for years until the 365 Suite finally accepted the legacy accounts, even on a Mac -- after years of waiting!). I expect the same to be the case in 2024 -- for a while, just a few millions of disgruntled users will complain, and Microsoft will safely assume that the issue is only "user error" and not worth pursuing further. But at some point, the daughter of a member of the Board will bump into this issue and then, in record time, everything will get fixed....

That is my hope right now :)

Because, frankly, it seems and feels stupid to be using the New Outlook for reading and sending email for essentially all possible platforms and accounts (and I do have many!), with the sole exception being... Microsoft themselves :(

How come they didn't fix this problem??? It's been reported since August 11 2023. I'm considering switching to google services for cloud and everything else.

You don't have any aliases on your Microsoft Account?

I keep getting sent back to the begining, Outlook let me add one of my Email addresses but not the 2nd. I also was able to get into my 365 account ( finally ) but that did not help

This same issue happened on my Outlook Office app. My son-inlaw, ( Microsoft employee ) also failed to get the account add. Also contacted my Service provider with no help.

I use to have this all work, but believe the issue started with an update from Microsoft.