I usually install mail servers to my clients. These customers generally have a fixed IP address. So they are blacklisted with the time when sending emails to the outside. Finally I use their ISP's SMTP relay as creating an SMTP connector in Exchange for example.
So the messages out to recipients and are no longer blacklisted.
Some time later I see they are again blacklisted and I am compelled to write to the guys who fight against spam, and I work with their ISP history that informs the "police" if I can afford to indicating that it was they who sold the IP and are not normal users but spammers.
Through a post I realized that the mail servers sending mail without the field are not allowed and these emails are considered spam.
My question is: what are the security measures that can be taken to properly protect mail server to avoid blacklisted, although we configure an SMTP relay?
Bookmarks