Okay, this is new to me and only today I found about this:
On Steam, the way to send group invites has changed. Now the admins MUST BE FRIENDS with any Steam user BEFORE they can send an invite from the groups they manage... (yeah, yeah, I know... ¬_¬)
Source and official announcement, here:
http://steamcommunity.com/games/593110/announcements/detail/1446071197008661976 So for now, everything will stay the same, people interested in joining the group should post their requests as usual, but the difference now is, before I (or Adam, or any future admin) can send a group invite, a friend invite will be sent to the new members so a group invite can actually be sent to them via Steam. The "Steam Friendship" will be only temporary (to not clutter everybody's friends list), so once the friend invite has been accepted and the new members have joined the group, that "friendship" can be canceled later at any time by anyone (if anyone wishes to do so, no questions asked :P).