[exim] Problem with local_part_prefix

Hi,

I'm trying to set up the following router:

discard:
debug_print = "R: discard for $local_part@$domain"
driver = redirect
local_part_prefix = ftp
domains = +local_domains
data = :blackhole:
check_local_user

(I now the disadvantages of blackhole, but this is a special internal
configuration.)

If I delete the local_part_prefix line, the router works as expected.
But as you see, the router shall only be applied for local parts
starting with "ftp". exim4 -bt gives:

# exim4 -bt ftp0123@server
R: system_aliases for ftp0123@server
R: hub_user for ftp0123@server
R: hub_user_smarthost for ftp0123@server
R: userforward for ftp0123@server
R: procmail for ftp0123@server
R: lowuid_aliases for ftp0123@server (UID 1006)
ftp0123@server is undeliverable: Unrouteable address
#

Why is that? The "discard" router should follow "lowuid_aliases".

May it be the case that the prefix must end with "-"? (I come to the
idea because everybody uses it for "real-" etc.)

I only tried exim4 -bt, not a real message.

Thanks,
Peter