With Yahoo!’s major release of interface upgrades last week, three of the big four free e-mail inbox providers have now implemented important changes in the ways recipients can interact with mail. Only AOL has yet to go live with the full complement of new features currently planned. Earlier this year, Hotmail rolled out Wave 4 with Sweep and Time-Traveling Filters that penalize “gray mail” by sweeping it out of the inbox. Gmail’s new Priority Inbox now rewards messages that it deems most relevant to the recipient with preferred positioning in the inbox.

Yahoo!’s mail release, dubbed “Minty”, was rolled out to their customer base last week, with a slew of front- and back-end changes. The most noticeable changes are to the user interface, with a leaner, faster-loading (and more purple!) site that more closely resembles the mobile apps (read: iPad) versions of its offerings. The interface changes are designed to increase market share in non-US markets, where consumer broadband is not as common, and load times can still be an issue for larger percentages of the user base.

In addition, Yahoo! is giving stronger positioning to an existing disposable e-mail address feature. AddressGuard allows users to create disposable e-mail addresses to protect their main e-mail address. The disposable addresses can be handed out in lieu of their primary Yahoo! address, and mail received to the disposable addresses are delivered directly to the users’ inboxes or other folders (where they can be subjected to existing filtering). However, the user can disable the address without impacting mail to their real inbox any time they want, if they feel the disposable address is receiving too much spam.

AOL will take the wraps off of their own set of upgrades (named “Project Pheonix”) later this year. Few details about specific changes to the user interface have been confirmed, but insiders say we should expect tighter integration with AOL Instant Messenger, SMS messaging and MapQuest. They’re planning a Gmail-like archive feature and enhanced search across users’ e-mail folders. AOL say they will present fewer ads at entry points, but will serve up more targeted advertising when users drill down into AOL’s content sites.

A recent interview with AOL Mail Ops President Brad Garlinghouse also hints at a larger effort to deliver an integrated messaging platform for all of the users’ various inboxes – be they traditional e-mail inboxes at Yahoo!, Gmail or MSN, as well as IM, SMS or social media inboxes. He notes that Internet users now manage an average of 2.4 e-mail addresses, up from 1.9 five years ago. Garlinghouse intimates that Phoenix will position the AOL mail site as a hub for users to manage them all.

It doesn’t appear that either Minty or Pheonix include any major changes to the way they filter or deliver inbound mail. The message for senders is that social media and e-mail are converging quickly: Google’s abortive attempt to socialize e-mail with Buzz did not spell the end of other efforts, and it’s possible that more than one will succeed. If that happens, senders may have a better chance to turn their recipients’ entire social networks into prospects.

Andrew Barrett is Sr. Director, ISP Relations & Deliverability at Real Magnet