We have Exchange 2010 (v14.3 Build 123.4) running on SBS2011. When a meeting invitation is sent to some external users, it is received as an email containing the subject and body text, but the rest is missing (location, time, accept/decline buttons). Other external users receive the invitation as expected.
The problem is consistent in that a specific external user will either always or never receive the invitations properly. The external users report that they receive invitations from other organisations as normal.
Sending the invitations from Outlook 2003 or 2010 has the same result. In Outlook 2010, we have tried un-ticking the option "when sending meeting requests outside of your organisation, use the iCalendar format" but this makes no difference.
We use Exclaimer Mail Disclaimers so this was suspect, but it does not add a disclaimer to meeting invitations.
How can we troubleshoot this further? Thanks in advance!