Existing Site Mailbox users need not worry yet. Microsoft has not announced final retirement, and plans a migration option from existing Site Mailboxes to Office 365 Groups by September 2017
Announced dates
- March 2017 – Site Mailboxes blocked for new customers or site collections.
- June 2017 – Microsoft's next steps announced through Message Center
- September 2017 – Launch of a tool to migrate existing Site Mailboxes to Office 365 Groups
Error messages
Error when attempting to access the Site Mailbox application (Site Mailbox) v CZ a EN.
New Site Mailboxes can no longer be created in SharePoint Online. Use Office 365 Groups to connect email conversations to a team site.

New Site Mailboxes can no longer be created in SharePoint Online. Consider using Office 365 Groups to connect a team site with an email conversation.

Microsoft's statement
“We’re removing Site Mailboxes in SharePoint Online
Beginning March 2017, new SharePoint Online organizations will no longer have access to the Site Mailbox feature, existing SharePoint Online organizations will no longer be able to create new Site Mailboxes; however, any Site Mailboxes provisioned prior to March 2017 will continue to function.
What do I need to do to prepare for this change?
If you are using the Site Mailbox feature in SharePoint Online, you should consider transitioning to Office 365 Groups, to support email-centric collaborative scenarios.”

Komentáře