error 75, error 164

I am receiving the following error message:

Delivery error (command maildrop 18470 error (75, .mailfilter(164):
  Syntax error after ))) msg 4/1300 (24935 bytes) from
  <[email protected]>, delivery error
  (command maildrop 18470 error (75, .mailfilter(164): Syntax error
  after )))

but I have not yet spotted a syntax error in ".mailfilter".

I do not know where to look for the definitions of errors number 75 and
164; searching with Google has not provided an answer.

And I am confused by the mismatch in the number of parentheses in the
error message; there are only three opening parentheses but four closing
parenthesis:

   (command
   (75
   (164

   164)
   after )))

Am I misreading the error message?

RLH



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