When I set up my first web server on my own VPS, I took a step-by-step approach, gradually adding more features and more security and testing at each stage that I hadn't broken my web sites.
I thought I could take the same approach with my mail server, starting with a very simple server with minimal configuration, then adding security features one at a time, testing at each stage that my email had not been broken.
Unfortunately, there are many sharks in the sea, Internet bad actors ready to take advantage of an incompletely set up system. From the mail logs, it’s sobering to see how, within minutes, your new mail server immediately comes under attack from malicious third-parties wanting to use your server as a relay, or wanting to send your email accounts phishing emails, or wanting to spoof your email address and so on.
One problem I experienced was my server being bombarded with phishing messages to guessed account names, such as admin@ webmaster@ accounts@ info@ david@ susan@ and so on. There were so many spoof messages that receipt of legtimate messages was being delayed by several hours! Eventually this and other problems caused my mailserver to be blocked by gmail and hotmail, who refused to receive any emails from my ip address. I was forced to erase my VPS configuration and start again with a different ip address.
The correct approach is to immediately lock down the newly-installed mail server, then add a multitude of security procedures to foil attackers. Only when these are in place, should the mail server be activated and tested. These procedures are described in full detail in my two manuals, describing how to configure web and mail servers on a Linux VPS. The manuals can be purchased at my author website: Unusual Mysteries - Cookbook They are not expensive and will repay your investment of a small amount of cash in both time and trouble saved.
