Consider the following scenario. Your mail submission Uniform Resource Identifier (URI) is the same as the email address of a security group or a distribution group. You send an instant message to another user in Microsoft Lync 2010. In this scenario, your instant message is not delivered.
Note This issue does not occur if the user searched for you in Lync 2010 before you send the instant message.
This issue occurs because the security group or the distribution group is returned instead of your contact when another user searches your mail submission URI.
To resolve this issue, install the following cumulative update:
2496325 Description of the cumulative update package for Lync 2010: April 2011
To work around this issue, use one of the following methods:
Delete the email address attribute that is the same as your mail submission URI in the security group or in the distribution group.
Use a unique email address as the email address attribute in the security group or in the distribution group.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.