We have been inundated by emails from clients having a problem with the latest version of Outlook. Seems there is no quality control at Microsoft, and they let a bug through their update process.
The problem has been reported to us in different ways by a number of disparate clients. But the solution seems to be to download a new update from Microsoft, and/or to uninstall Outlook and reinstall it. When you reinstall it, Outlook will (or it should) get the configuration information from your domain’s DNS; all it needs from you is your log-in information, namely your email address and password, which you presumably have saved in your password manager.
We hope this helps you. This is not a problem with or caused by NinerNet‘s mail servers.
Updated, 2026-01-20: Believe it or not, there are better email programs out there, despite what Microsoft would have you believe. Unfortunately the email “app” I used to use when I still used Windows is no longer around, but Pegasus is. I intended to try out Pegasus before I switched to Linux, but I never did; however, it’s still around and very popular. There’s also Thunderbird, of course, but I have always hated that program.