Not since Edward I. Koch disclosed this year that he was suffering from a serious spinal ailment has his online commentary generated the volume of e-mail messages he received in response to his endorsement of Senator Barack Obama for president last week.

Most of the 400 or so responses to the endorsement were extremely positive, he said. About three dozen were not; some of them were downright vitriolic.

“I was surprised primarily by those who criticized me with the invective they used,” the former mayor said, “but I know those who praised me, had I come out the other way, would have used the same invective.”

“There is no acceptance of dissent anymore,” he lamented.

In his commentary, which is e-mailed periodically to roughly 4,000 subscribers, Mr. Koch, who has been a supporter of President Bush, wrote that “the country is safer in the hands of Barack Obama” and that though Sarah Palin, the Republican vice-presidential nominee, is “a plucky, exciting candidate,” it “would scare me if she were to succeed John McCain in the presidency.” He also commented on former Mayor Rudolph W. Giuliani’s “maniacal laugh” during his speech at the Republican convention.