Opera Mail

Opera Mail (formerly known as M2) is the email and news client developed by Opera Software. It was an integrated component within the Opera web browser from version 2 through 12. With the release of Opera 15 in 2013, Opera Mail became a separate product and is no longer bundled with Opera. Opera Mail version 1.0 is available for OS X and Windows. It features spam filtering (both automated and Bayesian), a contact manager, and supports POP3 and IMAP, newsgroups as well as Atom and RSS feeds.

Opera Mail uses one database that keeps an index of all mail, and sorts the messages automatically into several "views" or accesspoints. Messages are automatically sorted by type, such as mailing lists, and mail with attachments . This approach to indexing allows for quicker access to messages. For instance, a message sent to a mailing list with a word document attached will appear in both the "Documents" attachment view and in the "Mailing lists" view. Opera Mail can also use Bayesian filtering to automatically sort messages into other views. All messages in the database are accessed by opening the "Received" view.