Here are some steps that worked for me in converting a user mailbox to a shared mailbox.

Info: You can convert the following mailboxes from one type to another

  • User mailbox to resource mailbox
  • Shared mailbox to user mailbox
  • Shared mailbox to resource mailbox
  • Resource mailbox to user mailbox
  • Resource mailbox to shared mailbox

Example reason why you might wan’t to do this:

You have a mailbox account with the name of  bookclub and are looking make it a shared account because its consuming a license. To address this we will convert it to a shared mailbox account by issues the following commands in the Exchange Management Shell

 

If you have multiple accounts, the following steps may apply to you

 

Please note the following csv document formatting:

Ref: http://technet.microsoft.com/en-us/library/jj710164%28v=exchg.150%29.aspx