One of the most requested features in SharePoint Online in Office 365 is mail-enabled document libraries.
In the next major currently available update to Office 365 - Microsoft will bring you what is called Site Mailboxes.
The Site Mailbox is accessible from the site in which it is created. It allow access to users who are individually listed in the Owners and Members groups of the site - security groups or distribution lists are not supported by Site Mailboxes. The email address of the site mailbox will be generated automatically from the name of the site.
Site mailboxes are surfaced in Outlook 2013 and give you easy access to the emails and documents for the projects you care about. Site Mailboxes are listed in the Folder Explorer in Outlook 2013 (the rich client), letting you file emails or documents into the shared project space simply by dragging the email, document, or attachment into the site mailbox.
You will not see your site mailboxes when you sign into your mailbox with Outlook Web App. However, if you are in the default owners or members lists of the site you can use the Site Mailbox app to see an OWA web part that displays the messages in that site mailbox.
To set up a Site Mailbox for at site
1. Log into Office 365 Preview, click "Sites" in the top navigation bar and then click "new site"
2. Type the name of your new site, e.g TheMailHeavySite...
3. Click “Keep email in context” to install a brand new app called “Site Mailbox”...
The mailbox is being setup...
6. Select your prefered language and time zone...
The mailbox is ready, complete with a mail listing the email address of the mailbox - in this example TheMailHeavySite@modernoffice.onmicrosoft.com since my trial domain is modernoffice.onmicrosoft.com. People can now send mail to the site using that email address.
Back on the site home page you and other site members can access the newly created mailbox using the link created under the header "Recent" or by clicking "Keep email in contect"
If you open Outlook 2013 you will see the Site Mailbox(es) you are a member of listed in the lower left corner of the Folder Explorer in Outlook. Under each Site Mailbox a subfolder called "Documents" exists. You can drag attachments from any email to these "Documents" subfolders and they are automatically uploaded to the corresponding document library "Documents" in the SharePoint Online site to which the Site Mailbox is related.