Yahoo! paid $350M for the email system Zimbra because Zimbra offers a rich API for accessing every aspect of email workflow. This is the theory put forth by Richard MacManus in an excellent article on Read/WriteWeb.

The really revolutionary thing about this API is that it gives 3rd party developers the ability to not only access highly specific data within the email system and calendar system, but it also offers a platform for creating plug-ins.

This means adding features like

• Send message as an SMS
• Add contact to my Plaxo account
• Add contact to my friends and family list on Flickr
• Add Teqlo powered workflow
• Add content to a specific wiki page
• Add content to a specific Activity Centric Blog

This means that revolutionary functionality can be added in a way that is easily adopted by end users. Â Today, most workflows start with an email. Â You can try and get people to completely change their behavior and move over to an Enterprise 2.0 solution, such as Basecamp, or you can help them move gently and gradually out of their email client into hybrid Enterprise 2.0 solutions. Â The second hybrid method gets more traction faster.

Zimbra powered Yahoo! Vs Google

Richard mentions that Yahoo! is facing serious challenges in this area from Google. Â I think Yahoo! has a clear opportunity to do a very powerful end run around Google.

Gmail has no Plug-In API.  Today, it is not easy to build a 3rd party application that integrates workflow directly into Gmail.  For example, 3rd parties can not mark specific messages as read or archived if those messages where reviewed through the Gmail POP3 interface.  And there is certainly no way to build any of the kinds of plug-ins I suggested above.

If Yahoo! combines rich API access to their email service with a partnership with OpenSAM, which offers all sorts of Web 2.0 versions of MS Office, including the incredible EditGrid spreadsheet, they Yahoo! has a clear opportunity to deliver an extensible product that far out does what Google Apps has to offer the enterprise.

To Richard's final point, that is a lot of "ifs". Â And Yahoo! has had a great deal of trouble taking advantage of the new companies they have bought recently.

They clearly have the opportunity. Â Let's see if they take it.