Goals from Matthew Saunders on 21 minutes and birthday boy Luke Howell - 26 on Saturday - seven minutes after the restart secured the win for the Daggers.
Padraig Amond fired over early on but there was little to get the 1031 crowd excited after that.
Having found themselves 2-0 down Lee Molyneux was denied by Lewington but despite plenty of huff and puff they never really threatened a comeback.
It means the home side are anxiously looking over their shoulders after two wins in 11 games.
Richardson admitted: "I agree with the result, we did not deserve to get anything out of the game. The first 10 or 15 minutes, we were comfortable but then we conceded two terrible goals.
"Fair play to Dagenham, they did a job, they have no airs and graces, they played to their strengths and got the win.
"After that we had possession around the box but couldn't hurt them. But we have to remain upbeat, this is a big month for us, and we can't get too down."
Richardson also said he would talk to ex-England striker James Beattie this week about extending his contract which ends on January 9.
" I will sit down and speak to him," he said. "There is the geography and family considerations so we need to talk about this properly."