Using New Outlook on Windows for professional communication and productivity
I haven't read through all the posts but I'd like to make a suggestion to the reason for this happening even if I don't have a solution (and apologies if it's already been said). My wife and daughter both have hotmail email accounts - ie ending @hotmail.co.uk. I also have a hotmail account and it was my original email account. However after some years I changed my main email to a gmail account but I did not want to change my original hotmail account because that was what everyone knew me by, so I set up one of those things (I'm not very technical) whereby everything that would go to my hotmail account would be forwarded to my gmail account, and every email I sent from my gmail account would appear to the receiver as though it had come from my hotmail account.
To be clear, if my hotmail account was ******@hotmail.co.uk and my gmail account was ******@gmail.com, then every time I sent an email from ******@gmail.com, it would appear to the recipient as though it had been sent from ******@hotmail.co.uk.
This worked fine for many years until recently when, on sending messages to anyone on Yahoo, or sky.com or aol.com, it would be rejected with message saying it had been blocked due to sender being unauthenticated. I have yet to resolve this because it appears I have set stuff up called SPF or DKIM or DMARC or somesuch and so far it's been too technical for me (unless I pay someone...). Meantime I had got round this by sending to those people from my hotmail account rather than my gmail one, they would not then get rejected.
Around the same time, my daughter and wife were telling me that my emails to them in hotmail were now going to junk. I said to them, just click to say it's not junk, and then click to say never send emails from this person to junk (which had worked for me). They did this but my emails still kept going to their junk. Eventually I wondered if it was similar to the Yahoo etc problem because I was sending from a gmail address rather than my hotmail one. So I tested sending from my hotmail address and hey presto, the email went into their inbox and not junk.
So it would appear to me that unlike Yahoo and Sky and AOL where the email sent from gmail (but purporting to be from a hotmail address) gets rejected, Hotmail (Outlook?) doesn't actually reject it but instead sticks it into junk. And even though you might tell it not to put future emails into junk, if it's coming in appearing disguised as it were, tighter controls (I'm guessing) now will not let it through (unless I suss out this DMARC DKIM stuff).
So my guess is that the problem is the sender sending from a different address to that which it appears to show it's from. Just my four penny worth. And apologies if I've wasted anyone's time reading through this - but it might help someone.