Why is SMTP Insecure?

SMTP is a widely used default email protocol. Like Emails, SMTP is also insecure. Read this article to find out ways to secure your emails.

Generally, email is insecure and not the best medium for sending confidential files. But, it remains the primary means of communication for most people, especially organizations. SMTP is the most common protocol for sending emails. Furthermore, SMTP is unencrypted. This makes it a vulnerable protocol.

Most email clients use SMTP as the default email protocol. All the messages that we send through this protocol are unprotected because SMTP does not support encryption or authentication algorithms in its basic nature.

However, let's analyze SMTP and see how you can integrate security add-ons to protect your emails if your mail client uses this protocol.

What is SMTP?

SMTP stands for Simple Mail Transfer Protocol. It is the most common email transfer protocol used by most email clients. Its function is simple. It picks up your email and moves it through various servers to arrive at the recipient’s device.

The transfer process takes seconds. But since the protocol does not support encryption, anyone can trap the email that you have sent while it’s still on the way to the recipient’s device. The person can also alter or extract the details of the email.

Why is SMTP Insecure?

As stated earlier, SMTP is insecure because it doesn't support encryption or authentication algorithms. This makes it very easy for scammers to send malicious emails with spoofed addresses.

But then, a lot of email clients use this protocol. Hence, in a bid to make it safer and secure for email transfers, new security/authentication methods are introduced. Authentication methods such as Sender Policy Framework (SPF) and DomainKeys Identified Mail (DKIM) were all launched as a means of securing the SMTP protocol.

Threats To SMTP Security?

There are several threats to SMTP when it is used in its ordinary state for email transfer. These threats include:

  • Spam and Phishing: Scammers can get into your SMTP server and use your server to send malicious emails to your contacts and organizations. This act is called Open Relay.
  • Data Leaks: It is easy for scammers to hack into SMTP servers and extract information from the emails sent through the servers.
  • Virus and Malware Spread: Hackers leverage the insecure nature of SMTP to spread malicious software through emails.
  • DoS Attacks: It won't take serious technical skills for a hacker to get into an SMTP server and perform Denial-of-Service (DoS) attacks. This means flooding other email servers with lots of emails, which may lead to a server crash.

Can You Secure SMTP? How to Secure SMTP?

Although SMTP is insecure, there are many ways that you can secure SMTP. Let’s review a few of those.


Yes, you can secure SMTP using Secure Sockets Layer (SSL) encryption or Transport Layer Security (TLS) encryption. But, using SSL or TLS to protect your SMTP server requires a little tweak because SMTP servers use port 25, and SSL cannot connect to that port. So, you need to select port 465 for the setup to work.

Client-Side Solutions

Email clients deploy client-side solutions such as Pretty Good Privacy (PGP) and Secure MIME (S/MIME) to secure SMTP traffic and ensure that their users’ emails are sent through a secure network throughout the servers.

SMTPS (Simple Mail Transfer Protocol Secure)

SMTPS is a newer, secure version of SMTP that uses TLS encryption to ensure that emails are securely sent across servers to the recipient’s device. Put simply, it is a way of securing SMTP at the transport layer, by wrapping SMTP inside TLS.


The best thing you can do is integrate security features and add-ons to your SMTP server to protect the emails you send/receive. By encrypting SMTP servers, it becomes more difficult for hackers to decode and extract the data or information embedded in an email.

The email itself is insecure. It is left for you to secure your important data by leveraging newer email security technologies and solutions.