I have multiple Microsoft accounts, the one in question is the one I use to sign in to my Windows 10 computers.
When going to Outlook.com on any browser, any computer, my account is clearly found and credentials accepted, as is confirmed by the fact that I will be shown the authentication prompt:
OK, when authentication code is given, Outlook.com is trying to open my inbox for a minute, then this appears:
All other Microsoft services using this same email address are working perfectly. I sign in to all my Windows 10 machines with it, OneDrive and all other Office Online services work without issues:
From any other Office Online page I can open the web app selector, and select any other app than Outlook.com. All others work:
The issue is not causing me any bigger problems because this Microsoft account email address is created using a third party email address my Microsoft account being something like kari@MyOwnDomain.com instead of an @Outlook.com or @live.com address, which means that I in any case receive and check my emails on that account using other services than Outlook.com.
However, that Microsoft account email receives emails for aliases I have created for it, and now as I am trying to recover a password on a trivial non-important service, I noticed that I've used an alias of this account as my contact email for this service; as I cannot get to Outlook.com to check emails for this alias, I cannot receive the email to reset password.
All my other Microsoft accounts are working perfectly, both those created with a Microsoft email address (outlook, Hotmail, msn, live), and those created with a third party existing email address (Gmail, own domains etc.).
Can't sign in to outlook.com with one specific Microsoft account. All other online and in Windows installed Microsoft services and apps using the same account are working without issues, including signing in to Windows 10 using this account.
I have no idea how long it's been like this; I usually never sign in to Outlook.com with this account because as I told I receive emails for this address using other services. I only noticed it because I found out yesterday that an alias I have created for this Microsoft account has been used as contact email on one not too important service. Trying to recover password to this service yesterday evening was I believe first time in a month or two I have tried to check to sign in.
Any advice and tips about something to try welcome, Microsoft support has already been tried but the "help" received showed that even I know more about Outlook.com than their support staff.