3b2 sendmail problem with pipes

[Robertson John MAJ]

I'm trying to pipe mail to an automatic answerer on a 3b2/600.

The alias file is set up correctly.  Mailx (and sendmail directly) will
not recognize the pipe, but return the mail with the error:

CO: is not an identifier
|/bin/foobar... unknown mailer error 1

However, if I invoke sendmail directly with the -d8 debug switch
thrown, the pipe is handled correctly.

Any thoughts on what the problem might be?

Jack