Exposing the SMTP (Simple Mail Transfer Protocol) port to the Internet can pose a risk in terms of brute-force attempts -
attackers can use automated tools to guess usernames and passwords in order to gain unauthorized access to the SMTP server.
If an attacker is successful in obtaining the username and password for a legitimate user's email account,
they can use it to send spam or phishing emails, or to steal sensitive information.
An attacker using an organization's SMTP server to send spam or phishing emails can cause significant harm,
such as damaging the organization's reputation and leading to their IP address being blacklisted by email service providers.
If you are running an SMTP server on your Windows Server, you may notice that your SMTP logs contain thousands of
lines similar to the following:
These failed authentication attempts represent brute-force attacks on your SMTP server. If your SMTP passwords are not
strong enough, spammers may succeed in gaining access and use your server to send spam emails, which can result in your
server being blacklisted.
These attacks can also consume your server resources, such as bandwidth, CPU, memory,
and free disk space (SMTP logs may grow enormously).
can help you protect your SMTP server from brute-force attacks.
It works with any SMTP server software and can monitor either the SMTP ports or the server logs
to detect failed login attempts.
If the number of failed login attempts from a single IP address reaches a set limit (three by default),
the attacker's IP address will be blocked.
For Windows Vista/7/8/8.1/10/11 and Windows Server 2008/2012/2016/2019/2022