An SMTP hack abuses vulnerabilities found in the Simple Mail Transfer Protocol (SMTP), allowing hackers to rely on the victim’s reputation when sending spam and phishing emails. For example, when attackers hack into the SMTP server of Company A, they can send emails using the victim’s domain. These emails could contain spammy messages or malware but would look like they were from someone within the organization whose domain was used.
As a result, the hacked organization’s email domain or Internet Protocol (IP) address could be blocklisted. But this is just the tip of the iceberg. The victim’s reputation can get severely damaged because of the SMTP hack, causing clients to lose their confidence in the company.
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Suffering from an SMTP hack has negative consequences. Therefore, it’s crucial to understand what it is and know how to protect against it. To start, we’ll explain what an SMTP does.
What Does SMTP Do?
SMTP is one of the most commonly used protocols in delivering email messages over the Internet. Clients use it to send messages to servers, and servers utilize it to forward messages to recipients.
For example, when you send an email to a client, it gets sent to your mail server via SMTP. Your SMTP relay server forwards the email to the recipient’s mail server, again using SMTP. The recipient’s mail server would then forward the message to your client’s email address. This process is visualized by the image below.
What Is an SMTP Attack?
An SMTP attack is any exploitation of your SMTP server that enables attackers to gain unauthorized access to it. When an SMTP hack occurs, attackers can see the email addresses stored on your server and send messages to them while pretending to be you. The recipients, which can be clients or friends, will think that the email is from you since the hackers used your email address.
Aside from sending phishing and spam emails, an SMTP hack can also give way to denial-of-service (DoS) attacks. Hackers can use your SMTP server to send a massive number of emails to other servers, effectively drowning the targets until they crash.
An SMTP hack is made possible by exploiting vulnerabilities in SMTP servers. Attackers can gain unauthorized access to your SMTP server in several ways, including:
- Phishing and malware: A user within your organization may have downloaded a malware-infected file or clicked a malicious link, allowing threat actors to harvest their credentials.
- Physical access: A lost or stolen device can also be used to gain access to your SMTP server. Hackers can retrieve and breach email accounts on the device.
- Lack of encryption: Even without the help of malware or stolen devices, SMTP can still be committed since it does not use any encryption. Of course, your data is safe when accessing emails on Gmail or other email providers’ servers. But when emails are sent through SMTP, they can be intercepted by other people.
How to Protect against an SMTP Hack
Adding security layers to your SMTP server helps keep it safe from unauthorized access. Secure Sockets Layer (SSL) and Transport Layer Security (TLS), more commonly known as SSL/TLS, is a standard method of encrypting data sent through SMTP.
For utmost security, continuous education about phishing and malware should be advocated in organizations. Users should be aware of the current phishing methods that attackers employ. Bring Your Own Device (BYOD) policies must be implemented with caution and clear guidelines to avoid risks associated with lost or stolen devices.