Sometimes, you may find that your Internet Service Provider (ISP) will block port 25 and expect you to pay lots of money to unlock it. Well as is the way with computers.. where there's a will there's a way.
We came up with this solution because we had a client that wanted to rent out some of their surplus office space to a contact of theirs who wanted to bring their own server and exchange solution onto our network.
Well what did we have?
We had a Draytek Vigor, a fantastic bit of kit but not the best firewall out there, and a single static IP address. We needed to find a way to get two email servers, both fighting for the default SMTP port 25 onto one external IP. Just another small challenge for the IT team. More importantly though, where was our morning coffee?
A short while later and we had our coffee. Time to find a solution.
So here it is. Our lightbulb moment.
We found a great service from dyndns called Dyn Email Gateway located here: https://cgcookie.com/blender/2013/08/09/setting-up-a-render-farm/
The service allows us to purchase a service that we send our emails through to on port 25. Their server will then forward these emails through to you on a port of your choosing. e.g. port 2525.
To get started, go to the address above and select the Get It Now button as seen in the picture below.
- Enter your domain name
- Select the settings as required. The following settings we have chosen are
- Name Registration: None - We will leave our domain with our current provider
- DNS Services: I already have DNS services for this domain - DNS is done by our domain provider
- Email Routing: Dyn Email Gateway - this is the service we will be using to change the default SMTP port
- Select continue once selected
- Next we will enter the server hostname we want to send email through to. The DNS setting will be set at your domain provider via A record
- Select the check boxes for any additional features you require. Selecting spam filtering or anti-viral protection will increase the price.
- Once done, select how many years you require the service
- Complete the registration and pay for the service
- Once the service is configured, change your MX record at your DNS provider to point to the Dyn Email Gateway services that Dyn will provide to you
- Finally, ensure your firewall has been modified to allow the new port to route through to the servers internal IP address. You can either set your NAT routing to forward port 2525 on your firewall directly to the internal servers IP on port 25, or send to the server direct on port 2525. If you decide to send email to 2525 on the servers internal IP, you will need to configure Exchange to accept email on this port instead of the default port 25. This is beyond the scope of this guide.
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