aalaan wrote:

Doesn't seem to be it Brian. I only have a small address book, if
that's what you mean by contacts.

Certainly not. In Outlook, there is no "address book". The Outlook Address
Book is simply a view of your Contacts folder that shows those contacts that
have electronic addresses. When I say
"contact", I mean an entry in your Contacts folder, which is where all your
contacts should be.

Most of my emails out are sent as replies to those emailing me.

That's your explanation, then. The sender of the original message controls
what you'll see in the From field and, hence, what you'll see in the To
field when you reply.

I'm sure their full email address must
be sent (or else how could I reply correctly); it's just that I can't
see the whole address in the header of the screen, or on the list of
messages. I'm sure there must be a simple option I should select, but
it beats me at present!

You don't control how the other people's addresses appear when they send you
messages. Those people with names appearing in the From field set the Name
field in their account settings. Those people whose addresses appear did
not.
--
Brian Tillman