What are the Most Common Email Server Security Vulnerabilities?

Almost all of our data is stored on a server, making this an attractive target for malicious attackers. This goes even further for email servers as email is still one of the most popular ways of communicating online, especially for businesses.

If your email server is compromised and threat actors can gain access to the confidential information within it, this will result in financial losses for your company and losing valuable customers.

So let’s take a look at the most common vulnerabilities of email servers to better protect your data on them.

6 Most Common Email Server Vulnerabilities#

There are 6 most common email server vulnerabilities that you ought to pay attention to. These are:

  1. Data leakage
  2. Unauthorized data access
  3. DoS
  4. Malware
  5. Spam
  6. Poor performance and stability

Let’s explore each potential vulnerability and give you a way to prevent it.

Data Leakage#

Why do hackers attack email in the first place?

There can be several reasons, but the number one is that they want to get to the sensitive data of its owner (you, for instance).

The problem with email is that it was never built for security, but instead for ease of use. This is why your incoming and outgoing emails can be vulnerable to data leakage and a determined attacker.

The best way to protect your email data is to always use end-to-end encryption for both incoming and outgoing emails at end-points (sender and recipient), use TLS (Transport Layer Security) for emails in transit (while it travels between sender and recipient) and to use email protocols such as SMTP, IMAP and POP3.

Unauthorized Data Access#

No amount of encryption will save you if your last line of defense is weak.

What is this last line of defense?

Your password.

Unfortunately, only 35% of people use a different password for all their accounts, while 75% reuse the same password for all or some of their accounts, according to the 2019 Online Security Survey by Google and Harris Poll (yes, even Google says it's bad).

Now, expect that hackers will be even more inclined to try to bypass your email server’s authentication procedures to get access to the data in it, making password protection a must.

So how do you protect email server passwords?

The first thing you want is a strong password that can’t be easily brute-forced. That means at least 12 characters, including small and capital letters, numbers and special characters.

Here’s the difference that just 3-4 characters can make.

According to penetration testers at LMG Security, an 8-character Microsoft NT LAN Manager password can be cracked in less than 8 hours, while it would take 77,000 years for a 12-character password.

Denial of Service (DoS) Attacks#

Sometimes the attacker is not after the data that the email server contains, but instead wants to disrupt its service and prevent it from sending and receiving data.

Denial of Service or DoS is a type of cyberattack in which the attacker renders the server temporarily unavailable to its users by flooding the server with requests until the server can no longer cope with the traffic.

What is the solution?

Tprevent a DoS attack, you will need to limit how many connections you allow for the SMTP server, including both overall and simultaneous ones.


Like your personal or business email account, an email server can also be vulnerable to malicious software or malware.

In fact, malware will spread to the mail server via an infected email, which in turn was infected via an attachment most likely.

In order to prevent malware from infecting your server, you need to use third-party antivirus and antimalware security software like Kaspersky, Norton, etc, that are designed to detect, quarantine and destroy malware.


Although the ratio of normal-to-spam email messages in recent years has decreased from 71.1% of all emails being spam in April 2014 to that percentage being 45.37% in December 2021, according to Statista, spam is still a huge problem.

The main reason you might be sending email spam around is if you configure the SMTP server as an Open Mail Relay. This allows anyone on the Internet to send email (including spam) through your server.

To prevent this, configure your email server so that it only sends from authorized domains and IPs.

Poor Server Performance and Stability#

Email servers can at any moment stop working, their performance might decrease due to an attack or simple wear-and-tear.

To extend the lifespan of your email server and, more importantly, ensure uninterrupted service, you should enable SMTP authentication. This will protect the server from attacks in which the hacker sends numerous sent requests.

Additionally, you always need to have a backup server in case your main server stops working by having two MX records per domain.


As you can see, sending emails through a server is not always the best. This is why Telios email service allows you to send emails directly to the other person (via a peer-to-peer network) instead of through a server if they are online.

If the recipient is offline, Telios uses decentralized cloud storage to temporarily store your email until the other person is online.

Get Telios email today to protect your privacy and security.