Users accuse Yahoo of email 'trick'
Yahoo has denied that it has made it deliberately difficult for customers to migrate to another email provider.
It follows the disabling of an email-forwarding feature which allows people to migrate automatically.
Yahoo said it was a "temporary" move while it worked on improvements.
The firm is dealing with fallout from a massive breach of customer data and accusations that it allowed the US government to spy on emails.
In a statement to the BBC, Yahoo said: "We're working to get auto-forward back up and running as soon as possible because we know how useful it can be to our users. The feature was temporarily disabled as part of previously planned maintenance to improve its functionality between a user's various accounts. Users can expect an update to the auto-forward functionality soon. In the meantime, we continue to support multiple account management. "
But some of its customers were not convinced.
"This is all extremely suspicious timing," Jason Danner, who runs an information technology business in Auckland, New Zealand, told the Associated Press. He said that he was trying to leave Yahoo after 18 years with the email provider.
Such a feature has been "a basic concept for 15 years for just about every email provider out there", added technology business owner Brian McIntosh.
"All of a sudden it's under development. And only at Yahoo," he told the Associated Press.
There are also reports that customers of BT - which outsources its webmail hosting to Yahoo - are also unable to delete BT Yahoo email services.
A spokesperson told the BBC: "We apologise to customers who have been unable to delete their Yahoo account. We are working quickly to sort this out and expect to have this fixed soon."
In September, Yahoo revealed that hackers had stolen the personal information of half a billion people in 2014, a record-breaking theft that appears to have gone undiscovered for two years.
More recently there have been accusations that Yahoo opened its users' emails to government surveillance.
The New York Times said that the FBI scanned its users' incoming emails for an unusual string of characters that had been linked to a terrorist organisation. It added that the messages were made available to the FBI, but the scans have now stopped.
The details built on an earlier report by the news agency Reuters which said Yahoo had scanned millions of its users' emails on behalf of the US government.
In response, Yahoo said the Reuters report was "misleading" and that it was "a law-abiding firm".