How to search previous postings in sox-users ?

Whenever I have a question about something, 
I would like to first search for it in previous postings 
in case the question had already been asked and answered.

At the upper right corner of the sox-users homepage is a search-bar 
whose caption says "Search for software or solutions",
but that apparently only searches for "projects",
(not for previous postings in the sox-users list)

So, how can I search for certain keywords 
in previous postings of the sox-users list ?

...