Caro,
Neste caso funcionou:
$IPT -A FORWARD -s 192.168.0.91 -d loginnet.passport.com -j ACCEPT
$IPT -A FORWARD -s 192.168.0.80 -d loginnet.passport.com -j ACCEPT
$IPT -A FORWARD -s 192.168.0.81 -d loginnet.passport.com -j ACCEPT
$IPT -A FORWARD -s 192.168.0.89 -d loginnet.passport.com -j ACCEPT
$IPT -A FORWARD -s 192.168.0.82 -d loginnet.passport.com -j ACCEPT
$IPT -A FORWARD -s 192.168.0.83 -d loginnet.passport.com -j ACCEPT
$IPT -A FORWARD -s 192.168.0.91 -p tcp --dport 1863 -j ACCEPT
$IPT -A FORWARD -s 192.168.0.81 -p tcp --dport 1863 -j ACCEPT
$IPT -A FORWARD -s 192.168.0.80 -p tcp --dport 1863 -j ACCEPT
$IPT -A FORWARD -s 192.168.0.89 -p tcp --dport 1863 -j ACCEPT
$IPT -A FORWARD -s 192.168.0.82 -p tcp --dport 1863 -j ACCEPT
$IPT -A FORWARD -s 192.168.0.83 -p tcp --dport 1863 -j ACCEPT
$IPT -A FORWARD -d loginnet.passport.com -j DROP
$IPT -A FORWARD -p tcp --dport 1863 -j DROP
Falou,