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iptables -t nat -A PREROUTING -p tcp -i if0 --dport 143 -j REDIRECT --to-ports 8143
On FreeBSD, the rule is as follows:
ipfw add fwd 192.168.1.10,8143 tcp from any to any 143 via if0 in
On NetBSD and Solaris:
echo 'rdr if0 0.0.0.0/0 port 143 -> 192.168.1.10 port 8143 tcp' | ipnat -f -
