Yahoo is restoring its mailing service, which has been disrupted since Monday night due to a hardware problem, said the search engine giant.
According to the company, most accounts have now been restored while there was a backlog of emails yet to be delivered.
Yahoo said in a statement that the affected servers have been up and running and 30% of messages sent during the outage have already been delivered.
"We expect all emails to be delivered by tomorrow afternoon," a spokesperson said.
The internet giant said that most of the affected users should now be able to access their Yahoo Mail accounts on the web and apps for iOS, Android and Windows 8.
The updated mailing service, which was launched in October 2013, has been hit with several complaints regarding the elimination of key functions including 'tabs', in addition to several other technical issues.
The upgraded Yahoo Mail mailing service has reportedly been adopted by only a quarter of Yahoo employees, despite the management team's appeal to do so.