The Outlook I use at work tends to classify mail as junk if you get many, repetitive messages from a single source.
Such as "The website your company registered is about to expire" ;) Or, as in this case, messages from the forum here which are from a non-human source & of standard-ish format.
The trick is to go into the Junk folder, right-click on one such email, and pick "Never block sender". As I understand itm that'll prevent them from being classified as junk ever again. So make sure you let the right one in ;)
W.