If file does not exist, dot-forward exits 0. Versions of sendmail before V8 would throw away the incoming message. Normally file contains an address. The address is parsed as if it were in an RFC 822 message header. The dot-qmail delivery mechanism lets each user manage several addresses, so there is no need for a special syntax to get around forwarding.
Internet addresses can legitimately start with a slash or vertical bar.
This is dot-forward 0.71.