Gateway problem

[Brian Hawk]

I'm having a strange situation for quite sometime. I have two external 
interfaces one of which is an ADSL interface tun0 and obtains IP address 
dynamically and the other is a (xl1) leased line which has a static 
global IP address, lets say 212.64.212.180. Both interfaces access 
internet without any problem.

Recently I've configured qmail on this system to send out email thru xl1 
interface and use ADSL only for web traffic. It used to work quite good 
for a while but recently I noticed TCP packets have been going out from 
tun0 and responses coming in thru xl1. tun0 and ADSL is the default 
gateway. But the TCP packets are bound to 212.64.212.180 IP address 
which should send them out thru xl1. But it doesn't.

For the test, I did these

tcpdump -nt -i xl1 tcp &
telnet -s 212.64.212.180 smtp.tnet.com 25

connection establishes but I can see only the TCP response packets 
coming from xl1, like the following

x.y.z.t > 212.64.212.180
x.y.z.t > 212.64.212.180

All from external IPs to my xl1 int. No packets going out from xl1 they 
all go thru default gateway even if TCP connections are bound to xl1's 
IP address.

I'd like to know if anybody knows why this happened and I can I turn 
things back the way they were. Any help would be much appreciated.

My configuration is like this;

FreeBSD 5.4-RELEASE
ipf: IP Filter: v3.4.35 (336)
Kernel: IP Filter: v3.4.35
ipfw has no rules; allow ip from any to any
there's also a transparent proxy setup for squid

#~>netstat -rn
Routing tables

Internet:
Destination        Gateway            Flags    Refs      Use  Netif Expire
default            88.234.8.1         UGS         0 78722302   tun0
10/24              link#1             UC          0        0    rl0 =>
10                 10.1.1.222         UGS         0    26233    xl0
10.0.0.99          link#1             UHLW        0        4    rl0
10.1.1/24          link#2             UC          0        0    xl0
10.1.1.13          00:50:8d:ed:88:94  UHLW        0     1876    xl0   1118
10.1.1.222         00:01:02:df:c1:19  UHLW        1      689    lo0
10.1.1.225         00:b0:d0:20:b7:9e  UHLW        0    96690    xl0    706
88.234.8.1         88.234.14.26       UH          1        0   tun0
127.0.0.1          127.0.0.1          UH          0  2305904    lo0
192.168.0/16       link#3             UCS         0        0    xl1
212.64.212.176     ff:ff:ff:ff:ff:ff  UHLWb       0       15    xl1 =>
212.64.212.176/29  link#3             UC          0        0    xl1
212.64.212.180     00:04:76:9b:3d:f8  UHLW        0      125    lo0