The keeper pulled off a string of good saves in Richardson's first game in charge since being appointed boss on Wednesday, following a spell as caretaker manager.
Deeney made a double save from Blues' 12-goal top scorer Freddy Eastwood and Mark Bentley after just four minutes.
But defender Michael Whitlow collided with Deeney during the early action and was stretchered off with torn ligaments.
He was replaced by Shane McFaul, who went on to make a number of timely tackles in a decent performance.
Eastwood and Lawrie Dudfield both shot wide as the Shrimpers maintained the pressure before Notts replied through David Pipe.
County gradually exerted more pressure and saw Gavin Gordon head over Tony Scully's cross before Gordon headed Stefan Oakes' centre against the foot of Bart Griemink's left post.
But Southend had the final say of the half when Eastwood shot over.
Notts started the second half on the offensive with former Southend loan player Scully setting up Gordon for an attempt and then forcing a save out of Griemink himself.
But then the Blues created a hatful of chances that forced the best out of Deeney.
The goalkeeper saw a number of Southend efforts fly off target but then had to save shots from winger Nicky Nicolau and central defender Adam Barrett.
But Deeney saved his best for another double save as first he charged down an effort from substitute Southend winger Mark Gower and then save Barrett's follow-up.
Barrett thought he had added to his seven league goals for the season when he headed home Nicolau's corner from the right, but referee Kevin Wright ruled the attempt out for a foul.