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How to improve email security with S/MIMEs

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Phishing attacks are on the rise again, with some 83% of organisations experiencing a successful email-based phishing attack in 2021, up from 57% in 2020, according to Proofpoint’s 2022 State of the Phish report.  

What’s more, more than 65% of respondents also reported spear fishing and business email compromise (BEC) attacks, with 11% experiencing 10 or more successful attacks over the course of a single year.  

In fact, email security has never been so key to protecting your corporate data. It’s therefore vital that IT security leaders find ways to mitigate the risk of targeted attacks, ransomware, and the ramifications that come with these.  

In this blog, we’ll explore how S/MIME certificates can be used to improve email security; assessing what an S/MIME is, how it works, and how they can benefit your organisation.  

What are S/MIME Certificates? 

A S/MIME certificate, also known as a Secure/Multipurpose Internet Mail Extension (S/MIME) certificate, is an electronic file digitally signed by a Certificate Authority. When you use the browser and email application to decode messages containing this file’s digital signature, it verifies that the message’s sender sent it and it wasn’t altered in any way. 

S/MIME is a security protocol for sending encrypted messages via email that does not require the sender and receiver to share encryption keys or certificates. It is a protocol that ensures electronic mail messages’ confidentiality, integrity, and authenticity. 

The messages are encrypted with a recipient’s public key, and only that person’s software with their private key can successfully decrypt it. When sending an encrypted message, the sender’s computer generates a random symmetric key, encrypts the message data with this key, and attaches the encrypted key to it. The recipient can now read the entire message’s contents only if they have a private key that matches this symmetric encryption key. In other words, only if you know your private keys can you decrypt them. 

In general, S/MIME protects against unwanted modifications in transit or content interception. In some cases, it may provide additional mechanisms to recover discarded messages or prevent unauthorised access to key exchanges. A message sent using S/MIME will usually require some public key infrastructure to be valid. 

S/MIME also specifies a public key distribution system, a method for providing cryptographically secured public key certificates to senders and recipients and back-end support for secure key management. In this way, S/MIME is designed to facilitate digital signatures and encryption in electronic mail messaging. 

How does an S/MIME work? 

S/MIME is an encryption scheme known as an “end-to-end” solution that uses asymmetric encryption to safeguard email messages. This scheme involves two symmetrical keys known as the public and private keys. 

According to GlobalSign, an organisation that designs and focuses on Public Key Infrastructure (PKI) solutions to secure communications for commercial entities, the S/MIME digital signature method uses a public encryption key to communicate with encrypted messages. Only the intended recipient is welcome to use the corresponding private key, which is the only provider. 

In mathematics, the word “asymmetric” means that two unrelated keys are related mathematically. Traders use asymmetric cryptography for this reason: without the vital public key held exclusively by the sender, encrypted emails are almost impossible to decipher. 

A common criticism levied against how S/MIME encryption functions are that it tends to encrypt all the contents of an email, making it more challenging for antivirus/antimalware scanners to detect malicious software download sites and web links in a message. Some common security measures may make it harder to detect malware-based email attacks involving a legitimate sender’s email account. 

Key Features of S/MIME Certificates 

You receive numerous cryptographic security features when using a S/MIME certificate with your email applications which includes: 

Authentication: The S/MIME certificate allows you to prove your identity by digitally signing and encrypting email messages. This can help prevent email spoofing. The S/MIME certificate allows you to digitally sign an email message with your private key, which is required for other people to trust the message is authentic and has not been altered. 

Message Integrity: The S/MIME certificate allows you to digitally sign email messages using your private key. It ensures that the message contents and data inside that message were uncompromised. Corroborating the original contents of the message is significant for the decoding procedure. It is important to ensure that whatever remains inside the message keeps its integrity. 

Use Of Digital Signatures Invoking Non-Repudiation of Origin: S/MIME certificates allow you to digitally sign emails using your private key. The recipient of the email message can decode and read the original contents of that message because the integrity is maintained. They can verify that the contents have not been altered, they know it was sent by you, and they also know that you cannot deny having sent it. 

Data Privacy: S/MIME certificates allow you to encrypt email messages in ways that ensure that the message is confidential, as it will not reveal sender and recipient information, nor will it be stored in any local or remote databases. It also ensures that no third parties can get hold of information about the senders and recipients of emails. 

Benefits of S/MIME to Businesses 

With so many businesses operating online now, having a secure email communication system is key. S/MIME certificates help to protect these email messages and give an extra level of assurance through improved encryption. This measure has many positive results for organisations, including:

Business Reputation: Having obvious security measures like S/MIME certificates with encryption, email spam filter, and spam appraisal systems will benefit your company by keeping the business reputation. This is because customers will not have to worry about any information being leaked from your system and that you are trustworthy with their data. 

Minimising Business Risk: Many companies know that encryption in email messages is a necessary measure. With the S/MIME certificate, your company can take all necessary measures to ensure safe and secure communications. Your customers will feel more at ease because their confidential business information is fully protected from third parties such as hackers or employees; any plans and strategies are kept secret, and you never have to worry about having any of your business data leaked or lost. 

Avoiding Compliance Risks and Associated Fines: With S/MIME certificates, you can ensure that your emails are never lost and that some encryption always protects your messages. A few examples of this include GDPR (General Data Protection Regulation). This regulation is designed to protect your business information from being leaked or lost. Therefore, to protect yourself against fines due to non-compliance, you need to make sure you have a S/MIME certificate. 

Preventing Identity Theft: With the S/MIME certificate and encryption, your business will be protected from hackers and cybercriminals who are likely to target companies that do not encrypt their email messages for information theft. 


S/MIME certificates are a great solution to the problems of email security. It protects your business from losing sensitive information such as financial data, names and passwords, in addition to making sure that your customers feel comfortable and safe with the information they pass on. The fact that these threats are usually external such as cybercriminals, hackers and employees, makes a S/MIME certificate essential for any business that needs to stay ahead of cybercrime. 

Using S/MIME certificates will prove to be a great benefit for your business. It will benefit you, your employees and your customers. The S/MIME used by email applications ensures that no information is leaked or stolen from the business. It can be beneficial for your organisation to save money on expensive security measures and help protect the business’s investment in computers and software. The certificate also protects from financial loss caused by identity theft, intellectual property theft and more. Therefore, you can prevent these threats and have peace of mind by investing in a S/MIME certificate for your business. It is well worth it! 

To learn more about certificates, check out What are SSL certificates, and why do we need them? or the top 10 FAQs about the Jisc Certificate Service. If you have any queries, please feel free to get in touch with our dedicated service desk via  and we will be more than happy to help. 

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