[EXIM] unqualified recipient rejected

I'm seeing a lot of the following in my reject log with 1.750.
If the To: printed is the recipient line exim recieved, how is it
unqualified?

1997-11-21 14:11:47 unqualified recipient rejected: <23> H=ts26-13.tor.istar.ca [204.191.150.60]
To: santa@???

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  Artificial Intelligence stands no chance against Natural Stupidity.
            GAT d- -p+(--) c++++ l++ u++ t- m--- W--- !v
                 b+++ e* s-/+ n-(?) h++ f+g+ w+++ y*

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