Email system is not easy as you think to handle. You have built the email infrastructure from scratch and stable as it is. However in long run, few issue of attack has made your email server inconsistent. Some of those attack might cause your email server ip address blacklisted or low reputation. This was cause by issue such viruses infected by desktop/laptop in the network which the gateway IP address was being used by the email server also.
The other issue might due to user having simple password and email account had been compromised also being used for spreading spam through the email server using the ip gateway which some of the email will be fall under the spam trap and get blacklisted. And if the issue was not notify or not being monitor, this will cause the gateway IP to become low reputation. This will made your email server wont be able to send to any recipient or any email server out there in the internet.
I’m going to share how you be able to see if your gateway IP are blacklist or clean. Just need to browse through this url :-
As you can see below mainpage soon after you browse this URL. We will start mxlookup. This will help you to confirm your email server are using on which IP address at your server infrastructure. Just fill in your email server domain and click the “MX Lookup” button.
Now it will display the mx record of your domain. From here the first priorities or preference mx record is belong to your email server. Your may do 2 check (1 is blacklist check and the other is SMTP test). We will focusing on the blacklist Check.
Click on the “Blacklist Check” to proceed checking up if your email server IP address were blacklisted. Result are as per below :-
If all green this mean your ip were clean and if its bring list of red, this mean your ip were blacklisted. Some action need to be done and delisting are expected after action taken. I will elaborate the action and delisting step in next update.