How can I allow exim to listen on another port
Exim by default listens on port 25 which is commonly blocked by ISPs (Internet Service Providers) to help them address spam. Having exim listen on another port will make it so that you can use the other port to send email from your server instead of having to use your ISP's outgoing mail server(s) if your ISP is blocking port 25.
This article explains how to enable exim to listen on another port for virtual and dedicated server owners running cPanel. If you're a shared hosting client with Acenet, all of our shared servers are already configured to allow exim to listen on port 587 as well as 25. You can view more details on this here:
Here are the instructions on how to allow exim to listen on another port if you have a virtual and/or dedicated server running cPanel.
 Log into your server's WHM as root.
 Click on 'Service Manager' under the 'Service Configuration' section.
 Check mark the 'Enabled' and 'Monitor' boxes to the left of 'exim on another port'.
 Specify the port you want to allow exim to listed on in the text box to the right of 'Allow exim to listen on port'. We suggest port 587.
 Click the 'Save' button at the bottom.
You will also need to make sure that the port you specify is opened in any firewalls you may have installed on your server. Your server's administrator should be able to assist you with this.