An Alibaba Group Holding Ltd. manager accused of sexual assault by an employee has been fired, and two other employees, including a senior executive, have resigned, according to a memo to company staff from Chief Executive Daniel Zhang.

The allegations, which were published on the company’s internal discussion board Saturday, came from a female employee who said her supervisor, Wang Chengwen, brought her to a client event, pressured her to drink excessively and kissed and groped her against her will.

The 11-page account was shared widely on Chinese social media and sparked a backlash against Alibaba’s handling of the case from employees and the broader public. The woman, whose name wasn’t made public, also accused several Alibaba managers of mishandling the matter when she reported the incident and demanded that Mr. Wang be fired.

Mr. Zhang’s memo, which was sent internally to Alibaba employees Monday morning and later published by the company, said the accused manager had confessed to engaging in “overly intimate acts” with the accuser while she was inebriated and had violated company policy. He has been terminated and cannot be rehired, the announcement said.

Li Yonghe, president of Alibaba’s neighborhood retail business group, and Xu Kun, human resources generalist of the group, where Mr. Wang worked with his accuser, have resigned and bear some responsibility for the way the case was handled, Mr. Zhang said. Alibaba’s chief people officer, Judy Tong, will receive a demerit, he said.

Mr. Wang, Mr. Li, Ms. Xu and Ms. Tong couldn’t be reached for comment.

The memo included further steps the company said it would take to address such issues, including implementing anti-sexual-harassment training and investigation, creating a dedicated channel for employee reports and forming a zero-tolerance anti-sexual-harassment policy. Mr. Zhang said in his statement that the company opposes an “ugly” culture that forces employees to drink.

More than 6,000 Alibaba employees participated in an open letter to management on Sunday asking the company to set up a dedicated team and hotline for sexual-assault cases.

Some people took issue on Chinese social media with Mr. Zhang’s wording in his memo, particularly the description of Mr. Wang’s conduct with the female employee. “You describe an act of forcing a woman against her will as an ‘overly intimate act.’ Isn’t that an insult to the victim?” one user wrote on the Twitter-like platform Weibo.

Mr. Zhang said the police investigation in the eastern Chinese city of Jinan, where the woman said the incident took place, is continuing. Whether the former employee had committed rape or violated the law would be determined by law enforcement, he said. The Jinan police department said Sunday that it would update the public but didn’t disclose whether Mr. Wang was in custody or other details. Reached Monday, the police said to wait for a public statement.

The female employee didn’t reveal her identity in her account, although company employees said Alibaba staff who saw internal messages in which she alleged sexual assault would have been able to find out who she was.

She said in the account that police pulled surveillance footage that allegedly showed Mr. Wang entering her hotel room four times. She said she woke up in the hotel room on the morning of July 28 and found her clothes from the day before on the floor and an opened condom package on the nightstand.

She said police detained Mr. Wang after she reported him on July 28 and interrogated him for 24 hours. She said Mr. Wang told police that she had initiated sexual contact. On Aug. 2 she said she sought help from Mr. Wang’s supervisors but was later told by Ms. Xu, the former human resources generalist, that Mr. Wang couldn’t be fired.

Days before the Alibaba allegations, accusations against Chinese Canadian pop star Kris Wu renewed vigor in China’s fledgling #MeToo movement. Mr. Wu was detained after several women accused him of deceiving them into having sex with him. The move was lauded on social media and by women’s rights activists, since such accusations tend to be sensitive in China and run up against state concerns about disrupting public order. Mr. Wu denied the allegations and said he would willingly go to jail if they were true.

Discussion over sexual harassment continued to permeate Chinese social media on Monday, with state media leading online conversations around how to collect evidence of sexual assault and the drinking culture at business events.

People’s Daily, the China Communist Party’s flagship newspaper, took aim more broadly at unhealthy corporate culture on Monday, arguing that companies should focus on their values and winning the trust of their employees and the public.

“When faced with a crisis, instead of being ‘shocked, furious and ashamed,’ it’s better to reflect, review and act,” the paper said, referring to Mr. Zhang’s initial response to the accusation that he shared with employees over the weekend.

In his memo Monday, Mr. Zhang acknowledged cultural issues at Alibaba that he said he would work to change from the top, concluding the notice: “Please wait and watch.”

In less than six months, China’s tech giant Ant went from planning a blockbuster IPO to restructuring in response to pressure from the central bank. As the U.S. also takes aim at big tech, here’s how China is moving faster. Photo illustration: Sharon Shi The Wall Street Journal Interactive Edition

—Qianwei Zhang contributed to this article.

Write to Stephanie Yang at stephanie.yang@wsj.com