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I have configured a Squid proxy server on RedHat Enterprise Linux 5.4. All my Windows clients have been configured to use the proxy at 192.168.5.100, port 3128 when accessing the Internet.

However, Microsoft Outlook email clients are unable to access the Internet when sending or receiving email.

My iptables -P output is as follows:

iptables -t nat -A POSTROUTING -p TCP --dport 25 -j MASQUERADE
iptables -t nat -A POSTROUTING -p TCP --dport 110 -j MASQUERADE INPUT DROP  
iptables -A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
iptables -A INPUT -i 192.168.5.100 -p tcp -m tcp --dport 22 -j ACCCEPT
iptables -A INPUT -i 192.168.5.100 -p tcp -m tcp --dport 3128 -j ACCCEPT
iptables -A INPUT -i 192.168.5.100 -p tcp -m tcp --dport 25 -j ACCCEPT
iptables -A INPUT -i 192.168.5.100 -p tcp -m tcp --dport 110 -j ACCCEPT
iptables -A INPUT -i lo -j ACCEPT
iptables -t nat -A POSTROUTING -i 192.168.5.100 -o 192.168.1.100 -j MASQUERADE

My iptables -L output is as follows:

Chain INPUT (policy ACCEPT)
target     prot opt source               destination

Chain FORWARD (policy ACCEPT)
target     prot opt source               destination
ACCEPT     all  --  anywhere             anywhere

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination
`

Why is Outlook not working with the Squid proxy configuration?

  • Hello, let's add some more info about this, what gives you iptables -L ? what is your squid configuration ? if it is where is the iptable rule for this port. using masquerade plus a proxy is a bit strange in my opinion use either one or the other solution. Also what are you trying to do clearly, because you're goal not really identify here. – Kiwy Apr 2 '14 at 8:33
  • Also what are you trying to do clearly, because you're goal not really identify here – Kiwy Apr 2 '14 at 9:40
  • @Kiwy my goal is to allow my windows client machines to use microsoft outlook – BlueBerry - Vignesh4303 Apr 2 '14 at 9:46
  • as mention in the chat, Do you want to use an exchange server or just SMTP and IMAP ? what is your squid configuration ? you should first try to figure out what's not working before enabling iptables filtering. – Kiwy Apr 2 '14 at 10:37
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    Does turning the firewall off (service iptables stop) allow for the traffic to flow out? The squid proxy doesn't have anything to do with the Outlook email getting in/out. Squid is a HTTP proxy, for email that would be a SMTP proxy (i.e. a mail server). – slm Apr 2 '14 at 12:19

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