From a user account that is assigned to the CsUserAdministrator role or the CsAdministrator role, log on to any computer in your internal deployment.

Open a browser window, and then enter the Admin URL to open the Lync Server Control Panel. For details about the different methods you can use to start Lync Server Control Panel, see Open Lync Server Administrative Tools.

In the left navigation bar, click IM and Presence and then click File Filter.

On the File Filter page, click New.

In the Select a Site dialog box, click the site for which you want to create the file transfer filter, and then click OK.

In New File Filter, click the Enable file filter check box.

In File transfer drop-down list box, click Block All or Block specific file types.

If you clicked Block All, skip to step 10.

If you clicked Block specific file types, do the following:

1. Click Select to modify the default list of file type extensions that you want to block.

2. In the Select File Type dialog box, select the file types that you want to block or allow by adding or removing their extensions from the categories under File type extensions.

3. If you do not see the extension for a file type that you want to block, type the extension in the text box under Add file type extensions to the list, and then click Add.

4. Click OK.

Click Commit.