We had a web client user successfully using Mail Merge on a test web installation but after production was put into place Mail Merge failed.  With a little digging we discovered the initial download to install the Active Mail components places a .dll, Slxemailnotifier.dll, in the Windows\system32 dir and writes a registry setting detailing what web site the SLXclient opens.   The solution is to rename the Slxemailnotifier.dll, loggin to the SalesLogix web site using Active Mail.  There you will be prompted to download the Active Mail components again. Now the Mail Merge components will correctly point to the production web site.