Does
http://barn.homelinux.com/webmail work?
You haven't got esmith.barn.homelinux.com pointing to 62.79.78.12.
# ping barn.homelinux.com
PING barn.homelinux.com (62.79.78.12) 56(84) bytes of data.
64 bytes from 62.79.78.12.adsl.boet.tiscali.dk (62.79.78.12): icmp_seq=0 ttl=52 time=89.0 ms
# host -t any barn.homelinux.com
barn.homelinux.com has address 62.79.78.12
# ping esmith.barn.homelinux.com
ping: unknown host esmith.barn.homelinux.com
# host -t any esmith.barn.homelinux.com
Host esmith.barn.homelinux.com not found: 3(NXDOMAIN)
Sorry cant help with the filter error. Looks like some kind of error with the database that horde uses to store location info about your mail though.
HTH
Jimbo