Yahoo disabled automatic email forwarding at the beginning of the month, the Associated Press reported, citing several users.
While those who have set up forwarding in the past are unaffected, users who would want to leave following recent hacking and surveillance revelations are struggling to shift to rival services, the AP reported on October 10.
The company has been under scrutiny from investors after disclosing last month that at least 500 million user accounts were stolen from its network in 2014.
Reuters reported last week, citing sources, that Yahoo last year secretly built a custom software program to search all of its customers' incoming emails for specific information provided by US intelligence officials, a move that raised a lot of human rights concerns.
The AP said that several users were leaving or had already left the service because of the negative headlines.
Yahoo, which agreed to be bought by US telecoms company Verizon Communications Inc for $4.83 billion in July, could not be immediately reached for comment.
The company's website says that the "automatic email forwarding" feature is under development and has been temporarily disabled.
