SBS 2011 Cannot Send email to external domains

Posted on 2011-10-10
Last Modified: 2013-12-02
I just set up a new SBS 2011 server and am having trouble getting external email to send. I have found that the messages are stuck in the mail queue with a status of : "Retry"
The Last Error is the same for all which is: "451 4.4.0 primary target ip address responded with 421 4.2.1 unable to connect"
My ISP blocks port 25 so I changed the Send Connector port from 25 to 2525
I also added DNS forwarders of:, and (Google Public DNS)

Please help me resolve this issue.
Question by:jmolhava
    LVL 3

    Expert Comment

    Verify that the settings of your Default Internet SMTP Send Connector is correct in the Organization Configuration --> Hub Transport and is enabled.
    LVL 56

    Accepted Solution

    You cannot arbitrarily change the port of the send connector. The destination servers don't know they should be LISTENING on port 2525, herefore connections are failing. ISPs block port 25 to prevent rogue dynamic IP clients from being part of spam botnets. If bypassing that was as easy as using a different port, that wouldn't be very effective.

    You have two choices:

    1) get a business class service from your ISP. This usually includes a static IP and unblocked port 25.

    2) as long as running a mail server is not against your current ISP service terms of use, you can use a smarthost to relay mail for you. There is a wizard in the SBS console to configure a smarthost and it will use an alternate port (which you get from your smarthost provider) to avoid the port 25 block.



    Author Comment

    @stanley - There is only one Send Connector which was setup by the wizard during install.
    The FQDN is correct
    The address space is SMTP with "*" for domain
    Network is set to use (DNS) MX records to route mail. (no other options selected here)
    Server tab is correct

    LVL 10

    Expert Comment

    is the exchange 2003 server (or SBS 2003) still up?  if so, try using the Exchange 2003 machine as a smart host on the 2010 send connector.  

    Author Comment

    @cliff - That makes sense so I will have to go with a static IP option from our ISP. We are on a business line of service, but the static IP is an optional feature. I had changed the port because of another post elsewhere that talked about making that change. Thanks for clearing that up for me.
    I will be making the change tomorrow and will close this issue out assuming that it resolves things.

    @SuperTaco - The previous server was not an SBS server. Previously, email has been hosted through another company.
    LVL 2

    Expert Comment

    Moreover to get the default settings on Connectors you can run Fix My network wizard which will configure the send connectors to the default.


    Author Closing Comment

    Thanks for clarifying for me what was required. I did get a static IP with port 25 unblocked and now all is working well.

    Featured Post

    Do You Know the 4 Main Threat Actor Types?

    Do you know the main threat actor types? Most attackers fall into one of four categories, each with their own favored tactics, techniques, and procedures.

    Join & Write a Comment

    Learn more about how the humble email signature can be used as more than just an electronic business card. When used correctly, a signature can easily be tailored for different purposes by different departments within an organization.
    Use email signature images to promote corporate certifications and industry awards.
    In this video we show how to create a User Mailbox in Exchange 2013. We show this process by using the Exchange Admin Center. Log into Exchange Admin Center.: First we need to log into the Exchange Admin Center. Navigate to the Recipients >> Mailb…
    To show how to generate a certificate request in Exchange 2013. We show this process by using the Exchange Admin Center. Log into Exchange Admin Center.:  First we need to log into the Exchange Admin Center. Navigate to the Servers >> Certificates…

    734 members asked questions and received personalized solutions in the past 7 days.

    Join the community of 500,000 technology professionals and ask your questions.

    Join & Ask a Question

    Need Help in Real-Time?

    Connect with top rated Experts

    22 Experts available now in Live!

    Get 1:1 Help Now