When a meeting request is sent to a non-domain recipient, the request is delivered in HTML format with an meeting request attached as a message file. When the message file is opened, the "Accept", Tentative" and "Decline" buttons are grayed out and disabled. When the meeting request is sent to a recipient within the domain, the meeting request appears as it is supposed to. Note that meeting requests originating outside the domain behave as they are supposed to. What must be done so that meeting requests originating within the domain to recipients outside the domain may be accepted or declined using the buttons?SBS '03 StandardXP Prof SP3 and Outlook '03, or Vista Ult and Outlook '07 on clients.

Is this happening with all the users sending meeting requests out side the domain.If not , on the sender Outlook, please check: On the Tools menu, click Options, click the Mail Format tab, in the Internet Format box, click "Send using Outlook Rich Text format", click OK and then click Save and Close. After that, please let the sender send a test meeting request to the contact to check whether the issue persists.Also check this out , if this helps http://ureader.com/message/1471441.aspxRaj