Open Exchange Management Console from Start->All Programs->Microsoft Exchange Server 2010 -> Exchange Management Console.
Expand “Microsoft Exchange On-Premises” and “Recipient Configuration”.
Right Click on “Mailbox” and click on “New Mailbox”.
Choose “User Mailbox” and press “Next”.
Choose “New User” and press “Next”.
Tick “Specify the organizational unit rather than using a default one”.
Click on Browse and choose the OU for the user.
Fill in the First Name, Last Name, Name boxes.
Fill in the “user logon name” in the format <lastname><firstinitial>.
Choose a password and confirm the password, then tick “User must change password at next logon”. Then press next.
In the next window type an alias. In the format of <lastname><firstinitial>.
Then click “Specify the mail box database rather than using a database automatically selected” and choose the only database listed.
Click on “Next”, review the “Configuration Summary”. Then click “Finish” to close the wizard.
A status of Completed indicates that the wizard completed the task successfully.
A status of Failed indicates that the task wasn’t completed. If the task fails, review the summary for an explanation, and then click Back to make any configuration changes.
Then go into Active Directory. Find the users OU previously selected. Double click on the user object and assign any user or data access groups required.
Amend the DDI in the telephone system with the updated user information.
Amend both telephone lists in the Public -> Telephone Lists folder.
Send an email to the users line manager with username, password and email details. Letting them know that it can take upto 24 hours for email addresses to resolve and that the user will be required to change their password on first logon.