Is there no 'hide recipients' function?
Yes, that is the BCC function. Properly configured junk email and spam
filters in general will not drop such emails. Otherwise you can opt to use a
mail merge instead.
From where do you want to hide these fields - on the visible screen in
front of you, or from the message headers in the outgoing message? If
so, use Bcc, as indicated below.
My boss claims that when you are creating an email and you click on the "To"
field to access the Global Address Book, there is a tab in the bottom left
corner that is labeled "Advanced", there is a "send options" selection there
and you can choose a hide email recipients command from there, but I cannot
get it to work. Do you know anything about that option?