NEC member Ann Black said that only one in 10 people who contacted the committee did so to complain about the decision.
In an email seen by the JC, she wrote: "I have received thousands of messages, almost all cut-and-paste but running more than 90 per cent in support of the NEC decision.
"I agree that there are arguments on both sides, and will continue to listen."
Luke Akehurst, director of We Believe in Israel, a grassroots group which called on people to contact the NEC directly, said at least 250 pro-Israel activists had subsequently written to the NEC, with a further 400 emailing the Labour Party directly.
He said: "We know the NEC members received a lot of emails from the Palestine Solidarity Campaign, thanking them for the boycott.
"The PSC's ability to get people to take part in calls to action is very high."
