Email Security Intelligence - SSL/TLS for Email Encryption: A Comprehensive Guide on Email Security

Looking to secure your email communications? SSL/TLS protocols can help through enhanced email encryption and securing sensitive data. 

Phishing and ransomware attacks are increasing, leading to millions of losses for several organizations. For example, a magecart attack leads to a £183.4million fine for British Airways. Similarly, phishers use social engineering practices to target users and extract credentials, including email addresses, financial details, and phone numbers. 

Emails are a vital source for such phishers who create fake messages to influence users into giving their credentials. In 2021, 83% of organizations will suffer from phishing attacks. Most phishing attacks involve the usage of fake email messages.

So, what’s the way out?

SSL certificates are an encryption-based technology that helps secure the communication between sender and receiver. So, what is SSL, and how does it help secure your emails? Here are the answers with a comprehensive guide on email encryption, security protocols, SSL/TLS solutions, and best practices. So, let’s get started with the basics- encryption!

What Is Encryption? What Is Public-Key Encryption?

Encryption is a process of scrambling information so that only authorized users can access it. In other words, encryptions allow you to convert the data in plaintext into random arrays of alphanumeric values. Such values are hard to decode for a hacker and can only be decrypted through a security key that an authorized user will possess.

Every encryption process needs cryptographic or security keys, which are mathematical values. The information sender and receiver must have a cryptographic key for data exchange.

Public key cryptography is an encryption process with private and public keys. If the data is encrypted with a public key, the receiver will need a private key to access the data. Similarly, if the private key is used for encryption, a public key is required for decoding.

Let’s further understand how public key cryptography works. 

How Does Public-Key Encryption Work?

Public key cryptography works like a lock and key mechanism. It is a locker with two keys that you need to retrieve encoded data. In simple words, the sender of the information will encrypt the data through cryptographic encryptions. The only access is possible if you have the private or public key for that data for decryption.

Two significant aspects of public-key cryptography are security keys and cryptographic algorithms.

Security Keys

Security keys are mathematical equations that help in encoding and decoding the message. Let’s take an example of a CTO who wants to send important technical documents to the senior developer. If the message is not encrypted, it will be in plain text, visible to any hacker who can access the network or communication channel between the server and browser. 

The CTO needs to encrypt the email with a public key and send a private key to the senior developer to access the confidential information. But, how does he or she ensure that the data is secure and encrypt it? This is where a cryptographic algorithm comes into play. It helps in applying the mathematical equation to scramble the data.

There are two ways to use security keys depending on the type of encryption.

Symmetric Encryption

Symmetric encryption has the same security key for encryption and decryption. So, you don’t need to assign a public key and a private key separately. 

Asymmetric Encryption

On the contrary, asymmetric encryption, also known as public-key cryptography, uses a security pair for encryption and decryption. It uses a public or private key for encryption and decrypts the message sent between sender and receiver. 

The algorithm is the second and one of the essential parts of public-key cryptography.

Cryptography Algorithms

Cryptography algorithms help alter the information from a readable format into a more random array of values. They are used for different use cases like data encryption, user authentication, and digital signatures.

There are many types of cryptography algorithms that are used for different purposes. Some of the most used algorithms are: 

  • RSA algorithm is a cryptographic algorithm used for encryption based on the block cipher concept. Many certificate authorities use a popular algorithm for digital signature and SSL certification.
  • DES algorithm is an algorithm that helps secure information through the block cipher concept but with symmetric encryption. 
  • Hashing algorithms enable you to convert the files containing critical data into a secure asset. It performs hashing, converting the file information into random string values, which are hard to crack for hackers. An attacker can only access data from the hashed file through a brute force attack.

Now that you know what encryption is and how it works, let’s understand how it can help you secure email.

How Can I Use Encryption to Secure Email?

Email is one of the most significant modes of communication for business and a popular target for hackers. According to Deloitte, 91% of all cyber attacks begin with a phishing email. So, there is no denying that you need reliable email encryption to avoid any such attack or exposure to your confidential data. 

There are two types of email encryption popularly used for securing the data, 

  • Encryption in transit
  • End-to-end email encryption

Email Encryption in Transit

Encrypting the email in transit can help protect your data from Man-in-the-Middle (MITM) attacks. You can use SSL/TLS encryption to secure the email during transit. A user sends data through email is encrypted using Transport Layer Security (TLS). 

Take an example of Gmail encryption. The email platform supports enhanced S/MIME (Secure/Multipurpose Internet Mail Extensions). Both TLS and S/MIME need the sender of email and receiver to be on the platform that supports the same encryption. So, if you send an email through the Gmail app, the receiving party must have a platform promoting S/MIME. 

Especially for enterprise-level workspace setups, you need to have advanced email security. This is why it becomes essential to have SSL/TLS or S/MIME encryption for your email. Another necessary encryption type for email is end-to-end encryption.

What Is E2EE (End-to-End Encryption)?

End-to-end encryption (E2EE) is a type of encryption that keeps the data of emails private from everyone except the sender and target recipients. So, when E2EE is used, only the desired receiver gets to see the information decrypted. It is end-to-end, with the sender at one end and the receiver at the other.

E2EE is like a confidential letter that goes through the mail in a sealed envelope and is for the receiver’s eyes only. A postman or any member of the postal service is not allowed to access the email information. 

Many tech giants like Facebook, WhatsApp, and Zoom use end-to-end encryptions to exchange chats among users safely. End-to-end email encryption is based on the same approach. 

Despite its popularity, E2EE has been embroiled in several controversies. For example, the UK government has been trying to ban E2EE for investigation restrictions. End-to-end encryption does not allow service providers to share data with the government. 

So, the UK government wants to enforce the Investigatory Powers Act, which asks Communication Service Providers (CSPs) to store every data of users on the internet and share it with the authorities. 

So, how does it work?

E2EE works on the principle of shared keys. For example, you are sending an email to your manager to send a sales report. E2EE allows you to keep this conversation private by using shared keys. 

Both you and your manager share public keys for encryption. Now you and your manager also have a private key that matches the public key to form two shared keys. These shared keys authenticate and facilitate the exchange of data with decryption capabilities. These shared keys are constantly updated and erased to avoid exposure.

So, a hacker may have access to your conversations but can’t see the data due to the unavailability of shared keys to decrypt it. Instead, the data exchange between two endpoints will be through a server. E2EE ensures that even if an attacker gets access to the server, the data stays confidential due to shared key encryption.

Now that you know how encryption can help secure your email and the different approaches for email encryption, it's time to understand which one to choose!

Choosing the suitable email encryption depends on the specific requirements of your organization. Both E2EE and TLS allow you to secure emails. However, there are security issues with the E2EE, which many governments are flagging now. In addition, E2EE is not accessible to governments and authorities, so there are possibilities for misuse. This is where SSL/TLS enters the game.

What Is an SSL Certificate, and Why Do You Need One?

Secure Socket Layer (SSL) is a technology that helps you secure communication between a browser client and a server. If you consider email security, an SSL makes sure that no data in your mail is exposed to MITM during the transit. There are two primary purposes for which you can use SSL certificates in email:

  1. Authenticate and verify the identity of the sender
  2. Maintain the integrity of email content

One of the most important use cases for an SSL certificate in email security is ensuring that your communication with the mail server is secure. Hackers can take control of the mail server and access your emails. 

So, how can you ensure that your email is safe?

One way is to install an SSL certificate and encrypt emails. It will secure your emails against any type of MITM attack. 

Here’s how to get an SSL certificate from a trustworthy SSL certificate provider:

Step 1: CSR Generation

The first step to get an SSL certificate is to generate a certificate signing request (CSR). Once a certificate authority receives the CSR, the vetting process begins.

Step 2: Vetting Process

CA will vet your organization and its details, including location, business aspects, legalities, and more. However, it depends on the type of SSL certificate you requested. Take an example of the Organization Validation and extended validation certificate. You will have to furnish several business details to the CA for the vetting process for issuing the OV certificate.

Step 3: Installation

Once CA vets, your organization gets an SSL certificate issued and sent through mail or available in your account on their official website. Either way, you can download and install the certificate on your mail server to secure the emails.

SSL certification will ensure that your data stays anonymous from hackers. One of the most critical aspects of an SSL certificate is the SSL/TLS security protocol. During email communication, SSL/TLS acts as an app layer protocol. 

It standardizes the communications for end-users and provides a set of rules that works with the Simple Mail Transfer Protocol (SMTP). So, you need to understand different security protocols for email security as they work in tandem to provide enhanced protection.

What Are the Different Email Encryption Protocols Available?

Standard email security protocols help you secure email transmissions. In other words, it allows you to ensure that hackers can’t read your emails while moving from a sender to a receiver.

Transport Layer Security

TLS is a successor to SSL(Secure Sockets Layer). It is an Internet Engineering Task Force (IETF) protocol that helps in authenticating email senders and receivers. Further, it also allows you to improve the privacy and data integrity of the emails. TLS is one of the most popular protocols used in different types of connections like: 

  • Web browsers
  • VPNs
  • Security of core network for 5G
  • voice over IP (VoIP)

So, how does Transport Layer Security work?

TLS uses a handshake between the client-side and server to establish encrypted connections. It ensures the security of communication and authenticates endpoints. Here is how it work:

  • Both sender of email and receiver exchange encryption capabilities
  • SSL/TLS certificates for both parties are authenticated
  • TLS protocol helps in establishing a secure connection

Now that you know how it works, here are some of the benefits of the TLS protocol:

  • TLS goes beyond the keyed message security provided by SSL through hashing-based message authentication, also known as the Hashing for Message Authentication Code (HMAC).
  • It defines Enhanced Pseudorandom Function (PRF), which employs two algorithms to increase data security. It is a type of failsafe where one algorithm is always active in case another fails.
  • Higher consistency in email security with TLS requires the specification of certificate type for data exchange.
  • TLS protocol is essential for FIPS 140-2-validated solution

SSL/TLS adds extra security to the SMTP protocol but does not end there. You need to know many other security protocols for enhanced email protection like TCP, STARTTLS, SPF, DKIM, DMARC, etc. 


When you send or receive emails, a Transmission Control Protocol becomes key to initiating the handshake between your client and mail server. The handshake undergoes several processes of security validations and encryption settings. 

Here are the steps for a handshake between the email server and client:

  • The client sends compatible email versions to the server
  • The server provides a TLS-based digital certificate and public key
  • The client verifies the digital certificate
  • The client generates a shared secret or pre-master key, which the server needs to decrypt.
  • On decryption, both client and server can now use the shared key to transfer data.


TLS operates as an application layer protocol. However, the sender and receiver need to have a secure communication channel. Therefore, STARTTLS is more than just a protocol; it's a security upgrade. 

It ensures safe delivery of the emails to the mail server from the client. STARTTLS protocol provides the server with the email client's information and a request submission for a secure connection. The best part about STARTTLS is its compatibility with legacy and modern TLS protocols. 


Sender Policy Framework (SPF) is a security protocol standard for email authentication. It helps define a specific way to validate an email sent by an authorized party. This is important as it acts as an identifier of the email sender. In addition, SPF assists SMTP, which is the primary protocol used for sending emails. 

SMTP does not have pre-built user authentication capabilities, and SPF helps authenticate email senders. 

So, how does it work?

SPF defines an approach the SMTP protocol needs to execute to ascertain that the email is sent from an authorized host. It uses Domain Name System (DNS) at its core.

  • Admin of the domain will publish the security policy(SPF Record) that defines the authorized mail server.
  • SPF records are listed as a part of DNS records
  • When an email is received at the server, it will look up the policies and allow only the ones with authorized senders to pass through. 
  • The server also compares the IP address of the email sender with the defined SPF record to ensure it's legitimate.
  • Receiving emails servers then look up the set of policies defined in their SPF record and decide whether to accept or reject the message.

As you can see, one of the essential parts of SPF protocol is the record. Therefore, it includes a database of the organization’s DNS. In other words, it has all the DNS details to compare the incoming emails and verify legitimacy. 

Here is an example of the SPF record: TXT "v=spf1 -all”

The above text explains how an email that claims to be from “” is to be validated from the SPF records. The prefix “v=spf1” indicates SPF record.” Further, it specifies the mail server SPF records through “”. Often times this might be the mail servers used by your email service provider, such as Gmail or Mail Chimp.

Finally, the “-all” part of the SPF record indicates that this is the complete list of servers authorized to send mail for your domain. Mail sent from other servers should be rejected by the recipient domain. This helps to prevent spoofing, but can also reject legitimate mail unless you're completely sure you've included all mail servers that send mail for your domain.


Domain-based Message Authentication, Reporting & Conformance (DMARC) is an email security protocol to secure mails. It depends on Sender Policy Framework (SPF) and Domain Keys identified mail (DKIM). DMARC uses SPF and DKIM to authenticate and verify the legitimacy of emails.

Similar to SPF records, DMARC records allow ISPs to secure email from social engineering attacks and domain spoofing. In addition, it will enable you to specify handling emails that are not authenticated through SPF or DKIM. This process allows ISPs to identify spammers and prevent malicious inbound emails into users’ inboxes.

Together, DMARC, DKIM, and SPF function like a background check on email senders, to make sure they really are who they say they are.

A DMARC policy determines what happens to an email after it is checked against SPF and DKIM records. An email either passes or fails SPF and DKIM. The DMARC policy determines if failure results in the email being marked as spam, getting blocked, or being delivered to its intended recipient. DMARC policies can contain instructions to send reports about emails that pass or fail DKIM or SPF.

A DMARC record stores a domain's DMARC policy.'s DMARC policy might look like this:

NameTypeContentTTL TXT v=DMARC1; p=quarantine; adkim=r; aspf=r; rua=mailto:This email address is being protected from spambots. You need JavaScript enabled to view it.; 32600

Now that we know all the security protocols for your emails, it becomes essential to analyze the implementation. Most organizations rely too much on SSL/TLS protocols and often ignore other necessary protocols. Although SSL/TLS does help in adding an extra layer of security, it has its restrictions.

What Are The Different Types of SSL Certificates?

Different Types of SSL Certificates Explained

SSL certificates can be issued depending upon the validation type that a customer chooses. There are three types of validation methods including Domain Validation, Organization Validation, and Extended Validation. The reason behind all three different validation methods is the level of verification that a certificate authority does of an organization. However, the more it is strict and of supreme level, the more customers would like to trust the site in a positive way.

What is a Domain Validation SSL Certificate?

Domain Validation is a basic level of SSL certificate where no legal documents are required to submit to a certificate authority (CA). To obtain a certificate, you need to verify domain control ownership. It can be done via verification of default email addresses like admin@, administrator@, hostmaster@, postmaster@, or DNS record email.

What is an Organization Validation SSL Certificate?

Organization Validation is a step ahead of domain validation where the domain validation process is performed along with deep checking of business related documents. The certificate authorities want to verify that the domain is related to the registered business. Once the verification is done, the CA issues a certificate. 

What is an Extended Validation SSL Certificate?

Extended Validation carries supreme validation where a CA validates the business by checking the business's legal, operational and registered status. If required, the CA can call on a registered telephone number for further verification. It activates a green padlock on a browser and customers can check registered company details with a single click on a padlock.

Variations of Certificates

Variations of certificates depend on the requirements of each website and the certificate is designed in that respect. Besides SSL types, there are wildcard SSL, multi domain certificates, and UCC certificates that secure from multiple domains to unlimited subdomains. For example, if you are specific for exchange server security, you will have your SSL certificate called a UCC certificate.

Multi-Domain (MD) or Subject Alternative Names (SAN) SSL Certificates

Multi domain certificate is a single certificate that can secure multiple domains and subdomains. There is no need to purchase a certificate for each domain or subdomain. The certificate comes with unlimited server licenses and unlimited re-issuance. 

Wildcard SSL Certificates

Wildcard SSL certificate is an ideal certificate for those who want to secure unlimited subdomains under the main domain. A site owner can add a number of subdomains once you purchase this certificate. The domain name should start with asterisk (*) and then all first levels of subdomains can be added. The main part is there is no need to validate each subdomain you want to add to the certificate.

Unified Communications (UCC) SSL Certificates

UCC certificate is a multi domain SSL certificate that can secure subdomains and domains. UCC certificate, however, is ideal for an exchange server environment, Office communication server, and live communication server. The certificate works with domain validation and organization validation methods. 

What Does Email Encryption Using SSL and TLS NOT Do?

One of the most common misconceptions is SSL/TLS is the silver bullet for your email security. However, SSL and TLS encryption do not protect your email from prying eyes. Instead, they can help someone track your email activity. 

Here's why:

SSL and TLS encrypt the data as it travels between your browser and the server. However, the encryption only protects the data while it's in transit. Once the data reaches the server, it's unencrypted and accessible for someone to read. Further, it doesn’t encrypt the individual message itself, only the path from the client to the server. 

So, before you generate your CSR and get an SSL certificate for your email servers, here are some critical limitations of SSL/TLS protocols.

SSL and TLS Attacks?

Like every other security technology, SSL/TLS has vulnerabilities. However, especially legacy SSL versions suffer from a lack of advanced protection against modern cyberattacks. Take an example of the SSL 3.0 vulnerability called the “Poodle Attack.” It is a vulnerability that exposes a weakness in the SSL 3.0, which ignores the padding bytes while running in cipher block chaining. 

Padding bytes are empty bytes added between the memory address and are aligned with the data stored in memory. Attackers can leverage such vulnerabilities and use binary padding to add malicious code and junk data to the memory. At present, TLS 1.2 is a current version that secures against such vulnerabilities.

SSL/TLS allows the client-side and server-side to decide which type of encryption they can use to make a connection. There is no denying that SSL/TLS does support robust encryption standards. 

SSL/TLS encrypts the communication and comes with an authentication. So, if an SSL channel is established, two endpoints from which the emails are sent and received can authenticate their identities. However, the issue with this mechanism is self-signed certificates. They are insufficient for enhanced security if the issuance is not from a standard CA. 

SSL/TLS Best Practices

SSL/TLS certificates are issued by CAs, which allow you to secure emails. Despite one of the most advanced security protocols and widespread usage, TLS can be exposed to several attacks. Here are some SSL/TLS best practices you should follow.

Choose the Right SSL Certificate Provider

Organizations need to choose a trustworthy CA for issuing their SSL certificates. Self-signed certificates are vulnerable. Further, if you choose a CA which is not trustworthy, your data will be at risk. Some of the leading CAs in the market include the likes of Comodo, RapidSSL, DigiCert, etc.

Use Physical Storage

An effective best practice is to store your private keys in Hardware Security Modules (HSM). These devices need to be FIPS compliant and highly secure. In addition, it allows your private keys to staying anonymous, which you need to get the SSL certificate issues.

Server Configurations

An effective practice you must follow is ensuring that servers are configured based on the domain and security requirements. For example, if you have more than one domain, you need to use Subject Alternative Name (SAN) to ensure they are secured.

SSL/TLS certificates have many use cases. However, the SSL/TLS term can be a little confusing for many organizations as it's mostly TLS in modern web app security.

Why Is It Still Called an SSL Certificate when We Use TLS? 

SSL is a legacy technology, and it's mostly TLS used by most organizations. However, it's just a naming convention that SSL certificate providers and businesses use. If you compare how SSL and TLS work, both need to establish a handshake mechanism for a secure connection. 

TLS is an improved SSL version where the handshake mechanism works only if the email's sender and receiver follow specific guidelines. Most importantly, it's the SSL certificate provider that matters as they can provide enhanced TLS security with the naming convention.

Now that you know all about SSL/TLS, security protocols, and vulnerabilities, it boils down to one crucial factor-your email certificate. It is the key to securing your emails.

What is an Email Certificate?

Email certificates are SMIME certificates (for MIME-based security), email signing certificates, SSL certificates, etc. It can have many names, but the function is simple- “identification & authentications.”

An email certificate is like identity proof you need to send or receive emails. Here is how it works: 

  • An email certificate at the core uses a PKI system to ensure that identity of the sender and receiver can be authenticated.
  • It also encrypts the contents of the email to prevent hackers from accessing it.

Lastly, email certificates are more than necessary in the modern era of several ransomware and malware attacks.


What’s more bewildering is how many organizations ignore email certificates for their sensitive communications. Email certificates and encryption technologies are not just protecting your data but also preventing hackers from exploiting your systems. Enterprises with massive internal communications need to rethink their security strategies, analyze the existing protocols, understand encryption and get SSL certificates for their systems.

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