The new version is being released globally, making it available in more than 38 countries around the world.
The development is the latest in a series of enhancements over the past year to make AOL Web Mail more open to third-party content and to offer increased opportunities to advertisers.
Ted Cahall, president, AOL Products and Technologies said: "Web Mail is an integral part of the AOL experience and at the heart of our product offerings. With this new release, we can showcase the important role AOL products continue to play in the company.
"Enhancing products that already attract a large, engaged audience is a key goal for our organization."
AOL Mail is the second most-popular free e-mail service, with more than 48m users.
According to Comscore, AOL Web Mail experienced a 27% increase in unique visitors in 2008 year-on-year, while Web Mail page views were up by more than 21%.
Along with third-party access, other changes to AOL's Web Mail product include:
- Increased speed and performance.
- Enhanced user interface.
- Themed skins.
- Plug-in gallery.
- AOL Sync -- real-time updates to apps such as AOL Calendar and Address Book from desktops or wireless devices, including the Blackberry and iPhone.