How to host email server if ISP blocks port 25? How to host email server ...

How to host email server if ISP blocks port 25?


The standard port used for SMTP connections is 25. An ISP (Internet Service Provider) may block port 25 in order to prevent spamming by its customers. With port 25 being blocked, you won't be able to host your own mail server at home or work. We will show you how to check if your ISP blocks incoming connections on port 25 and provide you with a simple and effective solution.

Frustrated Programmer

How to Check?

First make sure that your email server is indeed up and running on port 25 and port 25 is forwarded in your router and firewall. Then you can check if port 25 is blocked by your ISP by using one of these 2 ways:


Use our port check tool

First enter the hostname or IP address of your email server in Hostname or IP Address field, then enter 25 in Port field and choose the timeout value (default is 3), click Continue. If the result is Fail, chances are that your ISP is blocking port 25.


Use Telnet client

  • Check port 25 in Windows:

Open the  start menu ->  run -> type cmd and hit enter. In the windows command prompt type:

telnet 25

NOTE: Telnet client may be disabled by default, so you may need to enable it.

  • Check port 25 in MAC OS

Each MAC computer has a terminal client to execute command lines. Press the 'Command' key and 'Space' bar together to open spotlight, type in 'terminal' and hit 'Enter' to open the terminal. Type the following code in the terminal:

telnet 25

  • Check port 25 in Linux

Open your terminal application and type:

telnet 25

You should see a message similar to the following if it is not blocked: ESMTP Exim 4.80.1 #2 Thu, 05 Sep 2013 14:23:57 -0400 >

220-We do not authorize the use of this system to transport unsolicited,

220 and/or bulk e-mail.

If it is blocked, you will just see:  Connecting To… and it will fail after a while with Could not open connection to the host on port 25 Connect failed.

What is the solution?

If you run an email server at home or at work and your ISP blocks port 25, you can solve the problem by using our Email Store/Forward service. By using Email Store/Forward, you make our mail server your domain name's primary mail exchanger so that our mail server stores and forwards emails for your domain. When an email destined for your domain is received by our servers, we forward it to your mail server on an unblocked port of your choice. Not only does Email Store/Forward service allow you to run your own mail server, but it also does spam filtering and virus scanning. Finally, you get MX redundancy because our mail server will hold all your emails if your email server is unreachable. It continuously attempts to resend the messages back to your server until your server is back online.

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