Port 25 blocking

From Axentra

Some ISPs will block incoming traffic to port 25 (smtp) in order to prevent their customers from running a server. Some may also block outgoing traffic to port 25 to prevent their subscribers from sending spam. These blocks can prevent you from receiving email to or sending it from your Axentra Server, respectively.

Table of contents

1 Incoming Traffic 1.1 Diagnosing 1.2 Alternate SMTP port 1.3 Workaround 2 Outgoing Traffic 2.1 Procedure 2.2 Troubleshooting 3 See Also

Incoming Traffic

Diagnosing

• Ensure first that your domain name is set up properly, both on your Server and with your domain name registrar.
  • One way to test this is to look up your IP address at the bottom of the ISP Connection page in the admin area, and then attempt to connect to that address from the internet.
• Verify that you have not disabled "Sending and Receiving Email (smtp)" on the Network Services page of the admin area, and that you have not forwarded port 25 from the Port Forwarding page to another computer on your LAN.
• Most ISPs don't block all incoming connections. You should be able to access some features of your Server, such as the Jabber server, from the internet. (You can also try to ping your Server.) You may even be able to reach the admin area, even if you can't see your web pages. If you cannot connect to your Server at all, than you have additional problems.
• If your Server is behind a router or other gateway device, ensure that the device is not interfering with the connection.
  • Some modern cable and DSL modems act as gateway devices, so your Server may effectively be isolated from the Internet, even if it is directly connected to the modem.
    • Consult your modem's documentation to learn how to disable its routing capabilities, or to enable "passthrough" mode.
  • Place your Server in your router's DMZ if you haven't already done so.
  • If your router does not have a DMZ function, forward the appropriate ports through it to your Server. You will want to forward port 25, at least.

Alternate SMTP port

If incoming traffic to port 25 is being blocked by your ISP, you may be able to find another port which is not being blocked.

• Sign in to the admin area and go to the ISP Workarounds page.
• Enter an alternate SMTP port. It should be a number between 1000 and 65535. Some common ports to try are 2500 and 2525, though you may want to try a less common one.
• Click Apply to save your changes.
• From a computer on the internet, open a new Terminal or Command Prompt window, and type this command:

telnet domain.com 2500

substituting your own domain for domain.com, and using the port number you chose.

If you see a message similar to the following:

Connected to domain.com (11.22.33.44).
Escape character is '^]'.
220 domain.com ESMTP

then you've found a good alternate port. (Press Ctrl-], then type 'exit', to end the test.) If you don't get those messages, try a few other ports to see if you can find an unblocked port.

Workaround

If you have found an alternate port, then your Axentra Server will be able to receive incoming email, but not directly. You will need to use an external "mail reflector" or "email forwarder" service in order to be able to receive mail. Note that such a service may have an added cost.

• First, find such a service, and configure it so it forwards email to your server on the alternate port you defined. Consult the reflector service's documentation for details on how to do so.
• Then, instruct your domain name registrar to change its MX record to point at the email reflector service. Consult the reflector service's documentation for the exact domain name to use as the MX record.

If you could not find an unblocked port, then your only options are to inquire at your ISP about removing the block (this may involve an added cost), or to switch ISPs to one which does not do incoming port blocking.

Outgoing Traffic

Many ISPs block outgoing traffic to port 25 in an attempt to prevent their subscribers from sending lots of spam. These ISPs will still allow you to connect to their own SMTP servers to deliver your mail. You can configure your Axentra Server to send its email through that server.

Procedure

• First, get the address of the server from your ISP. It will probably be something like smtp.your_isp.com .
• Sign in to the web interface and go to the admin area.
• Go to the ISP Workarounds page, and scroll to the bottom. Enter your ISP's server name as your Outgoing Mail Server, and enter the username and password given you by your ISP in order to send email.
• Click Apply to save your settings.
• Go to the Email application and try to send an email to an address on the internet.

Troubleshooting

• If you receive a bounce message stating "Relaying denied", then you have incorrectly entered your username or password. Return to the ISP Workarounds page and retype them.
  • You might need to check with your ISP to see whether you need to add '@your_isp.com' to the end of your username.

See Also

• Port 80 blocking
• Internet problems