I had the same problem, and I solved it. Allow me to explain what I did, maybe this will help. I also use VPN (NordVPN), and it still works. I already had Outlook 365 installed on my computer from my college days (i.e. I didn't need to download it from GoDaddy, which I believe contributed to this problem). I had my Gmail, Yahoo, and school email accounts all tied into it. After I signed up with GoDaddy, I set up another Outlook email account with my new GoDaddy email. Kept getting that message whenever I would send an email from that account to Gmail, Yahoo, whatever. GoDaddy had me submit Microsoft delist requests, had me go see Google and Yahoo to fix it, etc. But they saw nothing wrong on their end. Webmail worked OK, but Outlook 365 didn't. I was about ready to request a full refund from GoDaddy. Then I discovered something. VERY long story short, do this: Open Outlook 365. Click File. Click Office Account in the left sidebar. Now look at "User Information" at the top of the left column. If that account is NOT your GoDaddy email account, that could very well be your problem. If this is the case: Temporarily shut off your VPN (yeah I know, but this is important and you'll be turning it back on in a minute). Click on "Switch account." A pop-up window will appear. Your GoDaddy email should be listed there along with your current user account. Click on your GoDaddy email account and the window will close. Now before turning your VPN back on, try sending some test emails. When I did this, my emails started sending correctly from my GoDaddy account to all domains. Once you can successfully do that, turn your VPN back on and try some more tests. Should still work OK, it did for me. Hoping for the best for all who need it!
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