Yahoo Mail users have been hit by service problems for over a week as engineers battle to repair an undersea cable.
The cable was accidentally cut during routine maintenance work leaving UK and US users unable to access their accounts and others facing slow page loading times. The worst affected regions appear to be eastern US and western Europe.
Sky and BT customers were also affected, as both use Yahoo to provide email services to their users.
"We are aware that Yahoo Mail is slow or inaccessible for some of our users. The issues were a result of an underwater fibre cable cut, caused by a third party while fixing a separate cable," the firm said on its status page.
"The engineering team has rerouted email traffic to mitigate accessibility issues. A cable repair ship has been mobilised and will be at the site this weekend."
The notice added: "Some Yahoo Mail users are experiencing delays in accessing and viewing their mail. We'll be posting updates regularly on this page to keep everyone informed of our progress. Thank you for your patience as we work to fully resolve this."
The firm apologised for the inconvenience and said it understood that email was "a critical service" for its customers.
Disgruntled users have taken to social networking site Twitter to vent their frustrations about the service problems.
"If yahoo was #rbs they'd be fined 56m for locking us out of our accounts. How am I expected to run my business with #yahoomaildown?" tweeted one angry user.
The firm has not yet said when service would completely resume, but users are advised to follow Yahoo's Customer Care Twitter account @YahooCare for updates.
Update: According to Yahoo Mail's status page, engineers have located the underwater cable affecting its network. "Testing and repairs are currently taking place. The Yahoo engineering team continues to monitor email traffic. Thank you for your patience," it said.
Users once more took to Twitter to air their disgust.
"Yahoo mail is down again. Can't send emails. Do you ever notice that you never hear that Google Mail is down? #yahoomail #yahoomaildown," said Twitter user Mark LoPresti.
