The Daggers were by far the better side and took a 3-0 lead into half-time, but did their best to give their manager a heart attack as the took their foot off the gas in the second half and let a poor St Albans side back into the game
Dagenham completely overwhelmed the Conference strugglers and took control of the game from the kick-off and could have scored after just two minutes when Sam Sloma's low cross was just missed by both Paul Benson and Mackail-Smith and Dave Theobold was there to clear the danger.
Moments later, Sam Saunders sent Benson clean through the gaping holes in the St Albans defence. But with just keeper Paul Bastock to beat, Benson blazed his shot over the bar from ten yards out.
But it didn't take long for the promotion chasers make their to make dominance count when Benson outwitted Magnus Okounghae as he tried to usher the ball out of play, he closed in on goal and pulled the ball back to Mackail-Smith whose shot was well saved by Bastock.
Sloma then followed up with a strike and all the keeper could do was parry his shot in to the path of the grateful Benson, who tapped home his 11th goal of the season.
The visitors simply could not cope with Dagenham's midfield pairing of Dave Rainford and Glen Southam, while Sloma and Saunders were causing havoc down the flanks. Benson and Mackail-Smith combined well to send Saunders through on goal, but he blasted his shot over the bar.
On 24 minutes, Benson outpaced the St Albans defence as he latched on to a Rainford pass, his clever lob beat Bastock but didn't come down quick enough to double his side's lead.
It was only a matter of when Dagenham would double their lead and it came moments later when Southam easily dispossessed Tom Davis and released Mackail-Smith whose venomous drive from 25 yards out flew past keeper Bastock for his third goal of the season.
Benson should put the game out of sight when the visitors gave the ball away straight from the kick-off and Benson once again found himself with just the keeper to beat, but he shot straight at Bastock.
Colin Lippiatt was obviously not happy with his side's display and made two tactical switches before half-time just to try and inject some life into his hapless side who were being totally outclassed
Mackail-Smith again wasted another chance when his shot across the keeper from inside the box.
The game was ended as a contest just before half-time when Rainford controlled a well worked short corner just on the edge of the area and smashed a stunning strike in the far corner of the net for his fifth goal of the season.
The visitors made a fist of the opening moments of the second half, but again it was the home side that made the chances, with Mackail-Smith again denied from close range by Bastock
Substitute Cliff Akurang, on for top scorer Benson who it seemed was being rested by John Still, created a chance for himself on the edge of the box, but again wasteful finishing let down the home side.
St Albans gave themselves a glimmer of hope on 66 minutes when Damian Batt's 25-yard shot crept inside Tony Roberts' near post.
The visitors took advantage of Dagenham nerves and could have got themselves right back in the game when Scott Griffiths should have cleared the ball but he tried to be cute and lost the ball.
Batt drilled the ball across the box and Paul Hakim cleverly flicked the ball past keeper Roberts, but it just went past the far post.
St Albans were making all the running now and came within a goal of Dagenham when a Alexis Nicolas free-kick was met with a towering Duane Jackman header which was pushed on to the bar by Roberts, Hakim reacted the quickest to stab the ball home from close range.
The visitors' hopes of a point were short-lived when Mackail-Smith eased the nerves of the home supporters when he headed home unmarked in the six-yard box from an excellent cross from Paul Bruce.
It's now seven straight home wins for Dagenham, who ran out worthy winners to keep up the pressure on Oxford at the top.