Under 1.8c you'd need to override the default filter (which is not
necessarily recommended, since you'd have to provide a substitute
explicitly in the list header, with "Filter= Only,...").  Personally
I'd consider this fairly dangerous.

Under 1.8d you will be able to specify overrides to the default filter
in the list header, eg,

* Filter= Also,[log in to unmask],Allow,[log in to unmask]

(although I think allowing <any> mail from an automatic service onto a
list is not a very good idea).  Note that the "Allow," part of the
filter specification MUST come at the end.  This is documented in the
current 1.8d beta manuals.

Nathan