Mackail-Smith told BBC Radio Cambridgeshire: "I don't know whether many of the boys read the forums or look at the papers.
"Sometimes it can be a bit harsh as we're going out there to do our best, but you have to believe in yourself."
Posh have slipped to 10th in the League One table, but remain just three points off the play-off places.
Boss Gary Johnson has previously told Posh fans to address their concerns directly to him, rather than at his players.
"Criticism doesn't bother me so much, but it does bother the players on occasions and they can get a bit disappointed," Johnson said.
However Mackail-Smith says he has been grateful for the backing they have received during recent matches.
"It's massive when the fans get behind us as it makes players want to get on the ball and do well," he said.
"Overall the crowds have been great given our recent results, but we need to start putting in some strong performances."
The former Dagenham & Redbridge man believes criticism is part and parcel of life as a professional footballer.
"You have to appreciate it's going to happen, people will have their own opinions and sometimes you'll need to take criticism on board," he said.
"People like to get onto me about my one-on-ones, but it's just a case of putting things like that to one side."
Source: BBC Sport
Source: BBC Sport