Everything You Need to Know About S/MIME Email Certificates

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Learn what S/MIME is and how it encrypts emails

With billions of emails flying back and forth every day, it is no wonder why it becomes such a hot spot for cybercrime activity. You could be sending your financial information, private photos, valuable intellectual property, and so on. And the last thing you want is to have your sensitive information intercepted via email.

Plus, your emails being intercepted isn’t the only email threat out there. There is also phishing. Phishing is when a cybercriminal sends an email with the intention to lure you into clicking on a malicious link or to give them sensitive information because you think they are someone else. With all these threats out there, I am sure you are wondering how you can better secure your emails. Lucky for you, there is something called S/MIME. In this article, we will dive into what S/MIME is, how it works, how you can get one, what kind of features they come with, and more.

What is S/MIME?

Are you wondering what S/MIME is? If yes, you are in the right place. S/MIME stands for “secure multipurpose internet mail extension” or “secure/multipurpose internet mail extension.” S/MIME certificates are digital email certificates that you can use to digitally sign all your emails. These digital email certificates will give you the assurance that the email you send can be read only by the intended receiver and no one else. You can send an encrypted email, then the receiver can decrypt and then your recipient can safely access the content of the email. The receiver of the email can also be sure that the email has not been tampered with.

Why Do You Need a S/MIME Email Certificate?

As mentioned earlier, emails we send can be tampered with by third parties like hackers. They can access an email and also modify its contents and steal sensitive information. But this will not happen if you encrypt your email with a digital email certificate. This way, you can be sure that the content of the email can be accessed by only the person to whom you sent it and not by anyone else. Similarly, email certificates also secure emails that are sent.

You might have come across server authentication SSL certificates that some email servers use. Though these certificates secure emails you receive from the secured server, they will not secure emails you send to a different email account on a different server. Unlike those certificates, S/MIME certificates offer end-to-end security and make sure all your email transactions are secure.

How Do I Get S/MIME Email Certificates?

You can get a S/MIME certificate from an SSL Certificate Authority. You just have to prove the email you use to register is owned by you by responding to the email the certificate authority sends to your email. Once you do this, the certificate authority will send you the email certificate that you can install in your email client.

How Does a S/MIME Email Certificate Work?

S/MIME certificates use asymmetric encryption to encrypt and secure emails. For example, if you are sending an email to your boss, you might not want anyone else to access the email as it could contain confidential business information. In this case, you would want to secure the email so that it can only be accessed by your boss and no one else.

You can secure your email by using a S/MIME certificate. Using a public key, you can encrypt your email. Anyone, including your boss, can have this public key. But no one can access your email without the corresponding private key. The email you send can be decrypted only with the private key. Only the intended recipient, your boss, will have the private key, using which he can access the email you send. This is all about S/MIME encryption.

You can get an email signing certificate from a certificate authority and digitally sign your emails and make them tamper-proof. These certificates will get attached to your email automatically soon after you make your purchase. The digital signature is associated with the public and the private keys. You will use the public key for authentication and the private key to generate the digital signature. This certificate will help the recipient understand that the email has not been altered or tampered with.

what is smime how it works

What Email Clients Can I Use with a S/MIME Certificate?

The following email clients support S/MIME certificates.

  • Microsoft Outlook
  • Apple Mail
  • Mozilla Thunderbird
  • Netscape Messenger
  • Outlook Express
  • Qualcomm Eudora

How Does a S/MIME Email Signing Certificates Increase Email Security?

With emails becoming more and more popular among the general population, it has already become an integral part of business communications. Over 300 billion emails are being sent every year, according to Statista. But we do not know how many of these emails are being hacked and accessed by third parties. Likewise, more than 90% of malware is being sent via email, according to Verizon. Most of the spammy emails slip through the defenses of email clients and land in our inboxes.

S/MIME will enable internet users to secure their emails and encrypt them. When you send an email with confidential information, you can be assured that S/MIME will secure the contents of your email and make sure only the intended recipient can decrypt the email and access its contents. Likewise, as S/MIME will let you digitally sign emails, you can establish that you are the authentic sender of the email. This way, S/MIME helps you stay away from hackers and man-in-the-middle attacks.

S/MIME certificates allow you to:

  • Encrypt the contents of the emails you send.
  • Establish that you are the authentic sender of the email by digitally signing your emails.
  • Help you avoid and stay away from email spoofing.
  • Prevent your sensitive information from being leaked.
  • Secure the data of your organization, employees, peers, colleagues, and clients.

You will see a lock icon which is the S/MIME Encryption level indicator, when you receive an email digitally signed using S/MIME. You will also see a check mark that indicates that the email is digitally signed. These indicators will help you recognize that the email is encrypted.

A private key is used to generate a digital signature. Using a public key, this signature will be authenticated. The public key that is sent along with the secured email will verify your identity. Each time you send an email, your private key will apply your digital signature. This is how the digital signature works.

What Other Features Are Included in a S/MIME Certificate Purchase?

You might be thinking, “wow, S/MIME certificates sound very helpful, but do you get anything else with them?” If you are thinking this, then you have a very opportunistic mindset and it is good for you. Some  S/MIME certificates do come with some existing additional features. These are not provided by all CAs, but here are some items to look out for if you’re interested in shopping around for a S/MIME certificate.

S/MIME certificates do not just secure and encrypt emails, but they come with certain additional features. Document signing and client authentication are two other features that come packed with S/MIME certificates.

Document Signing

You can use your S/MIME certificate to sign documents, in addition to signing your emails. Similar to how the recipient of your email can verify that you are the authentic sender of the email, people receiving your documents will also be able to verify that the document is from you. Using this feature, you can add your digital signature to your document and prove ownership. The recipient will be notified if the document is tampered with or modified as well.

Client Authentication

You can use a S/MIME certificate to secure your network and servers as well. While passwords can be easily stolen, you can take your security to the next level by securing your network and servers using this certificate. Using certificate-based two-factor authentication, you can secure your apps and the whole network. You can let only authorized employees access it and you can make it so only your employees who have a client certificate installed can access the network or servers.


By implementing S/MIME in your organization, you can be assured that all the emails you send and receive will be secure and encrypted. You can breathe a sigh of relief as you no longer have to wonder if third parties could access your sensitive information. You can also have the confidence that the contents of the emails can never be accessed or modified by anyone. If you still have not thought about email security, now is the time to seriously consider implementing S/MIME in your organization.

You can check out the DigiCert S/MIME certificate on our site. It comes with a host of excellent features (some of which we mentioned above) and it’s backed by the top CA in the world, DigiCert.

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