Browser-specific redirection error...
 

If you use the link in the emails to unsubscribe from a thread (my email is from read on outlook.com) and use Linux Mint 18.1/Firefox 53.3.x and you are ME, you get an invalid link error (outlook.com).

Doing the same thing from IE 11 works with no problem. If you were to click on the unsubscribe link again in IE you would normally get an invalid thread type error...

Since I had to go on the Windows box and open Outlook email to chack this out, it wasn't specifically from having two instances open at the same time.

This is also a new problem as last week's notifications behaved properly in this respect either way.

May be a false alarm or something I did.

I tried this. And for me, the first time I clicked the email link it did work. I re-subscribed to the same thread and tried the link again and I got the error as you described. I'll see what can be done.