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Sending eMail via alternate port 366 (Port 25 Blocked)

Many ISPs (Internet Service Providers) are blocking the standard SMTP port (tcp port 25) which is the port used to send eMail. They are doing this to cut down on the amount of SPAM that is sent from their networks.

Most eMail sent via the Internet is routed through the tcp port 25, the channel used for communication between an eMail client and an eMail server. Even though tcp port 25 blocking will probably become an industry standard, this practice can create problems for eMail servers and block legitimate eMail as well as SPAM.

NOTE: You may notice when you attempt to send eMail, that your connection is times out (connection timeout).  If everything else is working,  tcp port 25 blocking is a typical cause.

Here is how you can check to see if tcp port 25 is blocked on your network:

  1. Open a Command Prompt and enter:
    >telnet 25
  2. View Results:
    1. If tcp port 25 is unblocked, you receive a successful 220 response:

      Connected to
      220 ESMTP MAIL Service, Version: 6.0.3790.3959 ready at Tue, 15, Sep 2009 12:11:31 -0400
    2. If tcp port 25 is blocked you will get a connection error or no response at all:

      telnet: connect to address Connection refused.
      telnet: Unable to connect to remote host


DNN4Less offers customers the ability to send outbound eMail via alternate port 366.

When configuring your client software, there may be a specific box that indicates the port that should be used when sending eMail.  If it has not been modified, the port will be listed as 25.  By simply changing this number to 2525, your should be able to successfully send outbound eMails to our servers.

In situations where a box to specify the port number is not available, try entering “:366” after the SMTP host name…  Example: “”.

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  1. Senior Engineer Jessie

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