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My ISP has blocked all traffic to SMTP port 25. What can I do?


Some of my users are unable to send email because their ISP blocks all port 25 access outside of their network.

I want my users to continue to use my server rather than send via the ISP mail servers, is this possible?


SMTP Submission

You may find that despite blocking access to port 25, the ISP has opened a special, reserved port for its users to continue to send mail. This is known as the SMTP Submission port and by default is open on 587. From within your mail client you should configure your outgoing server to use port 587 and you should configure it to login with your account credentials.

Should this not work for you or you wish for your GMS server to listen on another port in addition to the well known 25, follow these instructions:


To enable this, first, logon to GMS as an admin and go to the Mail->Incoming->Connections page. From here, select “use IP connection file” and press configure.

You will see a warning which explains that this procedure cannot be reversed – accept this warning and move on, and you will be shown a list of the current rules – this is created based on the current configuration of your server. At this stage none of your existing settings are changed, merely transferred into the IP flexibility file.

To add a further SMTP port, click “add” then select “SMTP” from the service selctor.

now enter the options as follows:

Protocol: SMTP
Security type: NONE
Domain: select your domain
Hostname: enter your hostname – eg mail
IP address: enter your IP followed by : and the port id – eg
allow local clients (check this box)
external Ip addresses (leave blank)

In the example above, GMS will bind to IP on port 1025, in addition to the standard port 25.

Once you have done this, click finish and then go to the System->Control services GUI. Stop and restart the SMTP service.

You should now find that you can change your outgoing server SMTP port in your mail client to match the one you entered in the IP address dialogue, and you can then send mail to this new port.

Remember that if you have a firewall you will need to grant access to this new port to the server for this to work.

Keywords:ISP port ports 25 block access ipconnect

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