Consider the following scenario:
You have a user (use A) whose email address contains a hyphen (-) in a Microsoft Exchange Server 2010 environment.
You create a contact that contains a hyphen. The email address of the contact resembles the email address of user A.
You create an email message by using Outlook Web App.
You type the email address of user A in the To, Cc, or Bcc box.
You click the Check Names button.
In this scenario, the email address that you typed is resolved incorrectly to the email address of the contact. Therefore, you send the email message to the wrong recipient unintentionally.
For example, user A’s email address is email@example.com. The contact’s email address is firstname.lastname@example.org. You type email@example.com in Outlook Web App. Then, you click the Check Names button. In this situation, the email address is resolved incorrectly to firstname.lastname@example.org instead of email@example.com.
This issue occurs because Outlook Web App uses hyphens as word-breakers. Therefore, Ambiguous Name Resolution (ANR) performs ambiguous matching for the email address, and then selects the incorrect email address.
To resolve this issue, install the following update rollup:
2706690 Description of Update Rollup 4 for Exchange Server 2010 Service Pack 2
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.