Is there any way to see if an imap session is being routed through a proxy server.

Posted on 2011-10-11
Last Modified: 2012-06-22
I originally noticed the IMAP session failing on outlook express with a timeout error collecting the body of the email. So after further digging using other clients (thunderbird etc) I tested the connection over telnet.

I have reason to believe that the ISP is intercepting emails. Is there a way of proving that they are using a proxy to do this or some other device. I have a client that is with a certain ISP and when they initiate an IMAP session even using telnet, they are unable to retrieve the body of the email. The same mailbox works on any other connection and if you connect over VPN then the IMAP starts to work.

This scenario is being played out on mutliple connections from the same broadband provider from different locations and on different computers.

Also on any other connection using a different broadband provider  the imap works perfectly, but I need to prove to the client that something is happening with the connection that is intercepting or altering the way IMAP is handled, thus causing the error.

Any help would be greatly appreciated.
Question by:the_spudster
    1 Comment
    LVL 18

    Accepted Solution

    First, test if HTTP is proxied, Here is a web page, which examines headers and detects proxy:

    Another thing is to call ISP and ask, if port 143 for IMAP is maybe blocked. Some ISP restrict mail ports, mainly 25 SMTP to their mail servers only. But it might be that your ISP blocks all mail ports. They MUST tell you the truth.

    Might it be DNS problem?
    Try TELNET-ing to FQDN ( and also via IP ( If you get no response on any, then DNS is not a problem.

    Antivirus programs are also known to be problematic, but if you say the same client (laptop?) has no problems on another location, then this is not an issue.

    Maybe firewall or router?
    Some wizards on home routers have advanced DDOS and SYN atack and other protection measures built-in. You might try turning them off to see if this resolves issue.

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