How To Troubleshoot Server Not Accepting Any Mail

Introduction

If your server is unable to receive email, it could be the result of a firewall blocking port 25 inbound. Port 25 inbound must be open for your cPanel server to receive email.

Procedure

You can use the nmap tool to check whether port 25 inbound is blocked. Run the following command from outside of your server and replace '$serverIP' with the public IP address of your server:

nmap $serverIP -p 25

If the state shows 'filtered,' it would indicate a firewall is blocking inbound port 25.