Yahoo users will now have to switch to the search engine's new e-mail service, which is known to be the second or third most popular on the web.
Yahoo CEO Marissa Mayer had declared that it was awaiting a major overhaul of the e- mail service in December and progress has been made since then, CNN reports.
Addressing Yahoo users, Mayer said the company has listened to people's claims that they want fewer mail distractions and a quicker process of login and communication.
The mail upgrades have been facilitated for Web, Windows 8, iPhone/iPod touch and Android.
However, the change might face troubles, as some users are more comfortable using older versions including 'Yahoo Classic'.
They will be allowed to use the older version only until Monday.
The upgrading will need users to agree to terms, including 'automated content scanning' that will facilitate search algorithms to read through the content of people's messages in order to target relevant advertising, similar to the services in G-mail.
However, users can opt out of the feature by changing their settings.
The latest changes in Yahoo Mail will include removal of boxes filling the page in the Web version and offering thumbnail images of attachments, supposedly to help users in avoiding clicking on scams, spam and other unwanted content.
The iPhone mail users will be able to select multiple messages and swipe to delete, highlight or file the messages, the report added.