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Thread: Port 25 Blocking

  1. #1
    Join Date
    Apr 2006
    Rep Power

    Unhappy Port 25 Blocking

    Hi again folks,
    If I'm trying to run Zimbra on a residential DSL service and my ISP blocks port 25 is there a way of getting around this?

    When I speak to my ISP I get 2 different oppinions, some technical guys say that they do block port 25 others say that they do not. A search on Google says that most ISPs do block port 25 to avoid spammers and that includes mine (Bell Sympatico).

    Is there a way of redirecting Zimbra to use another mail relay available on the internet?

    thanks for your help.

  2. #2
    Join Date
    Oct 2005
    Harrisburg, Pennsylvania
    Rep Power


    Quote Originally Posted by gapnet
    Is there a way of redirecting Zimbra to use another mail relay available on the internet?

    There is, actually :-)

    If you log into the administrative part of Zimbra (, go into Global Settings, then MTA.

    Under MTA, you'll see an option for "Relay MTA for external delivery".

    In there, you can just list your ISP's mail server.... at that point, mail generated on the Zimbra server won't deliver directly, but instead will go through your ISP (smart-relay).

    Have fun,
    Last edited by andreychek; 04-12-2006 at 01:33 PM. Reason: fixed typo

  3. #3
    Join Date
    Nov 2005
    Rep Power

    Default Port 25 remapping

    IIRC, this will only adress the problem of outbound mail. Most ISP's will relay your outbound mail without issue, but it is unlikely that they will accept your inbound and relay it as well.

    If this is an issue, you can use a third party service such as DynDNS to remap your inbound mail to a port that is not blocked (DynDNS calls this service MailHop). Incidentally, you can also remap HTTP this way as well if your ISP blocks port 80 inbound.

    I have been using DynDNS remapping and Zimbra for many months now and have not had a single problem. In fact, due to reliability issues on the outbound MTA of my ISP, I have switched to using DynDNS for my outbound relays as well.

    There are other vendors out there that provide this capability as well, but I have not tried them.



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