Fellow MVP Peter Jamieson posted the following recently:

It is usually worth checking that Outlook is set up as the default e-mail
client, typically in IE Tools|Internet Options|Programs. Sometimes an
inability to connect to MAPI can be fixed by ensuring that the WIN.INI in
your Windows folder contains at least

[Mail}
MAPIX=1

and preferably

[Mail]
MAPI=1
CMC=1
CMCDLLNAME=mapi.dll
CMCDLLNAME32=mapi32.dll
MAPIX=1
MAPIXVER=1.0.0.1
OLEMessaging=1

However, if that stuff is not present, the merge to e-mail option in Word is
usually not enabled at all. So in your case I would guess that it is. If
so...

Where is mapi32.dll on your system?

Is it in any of the folders on the PATH?

You may be able to find out both these pieces of information by looking at
Word Help|About|System Info|Software Environment|

then Environment Variables|PATH for the PATH

and Loaded Modules, look for mapi32.dll

--
Peter Jamieson - Word MVP
Word MVP web site http://word.mvps.org/