Short version: "unknown mailer error" numbers are not standardized, not
likely to be common between any two independently developed mailing
systems, and probably not documented for any specific mailer.
 
Long version:
Usually, "unknown mailer error" means just what it says: that an error
occurred while running the mailer, but the author of the mailer did not
program in any special message (probably because the author believed that
it could never occur, or at least had no idea of what could cause it, but
know that if it happened it was an error).  For example, if your mailer
stores incoming messages in a certain coded format, then goes back to
read them and finds them not in that format (due to disk error, manual
editing, a bug in the encoding routine), the decoding routine might well
say something less than helpful to the end user.
 
The phrase "Options MUST PRECEDE persons" could indicate such an internal
confusion.  Neither "options" nor "persons" are standard terms for parts
of RFC821/822 mail on the Internet, but they do sound like they could be
the operands on a command in a Un*x-style system.  Perhaps an address
("person") is being mangled to look like an "option" (starting with a
dash, presumably), or somebody tried to include "options" in a forwarding
address?
 
Just idle speculation, except the part on the futility of trying to
assign meaning to the number some programmer assigned to "beats me"
or "oops".
 
Mark R. Williamson, Rice U., Houston TX; [log in to unmask] or @RICEVM1