An SMTP server is software that sends, receives, and relays email messages using the Simple Mail Transfer Protocol (SMTP) to transfer information from one mail server to another across the internet. Acting as the delivery tool for digital mail, SMTP servers process and deliver single, transactional, and bulk emails securely, enabling the billions of daily email communications that businesses and individuals rely on.
There are dozens of ways to communicate digitally today, yet email still stands the test of time. Email remains a prevalent way to communicate for businesses and individuals alike. An estimated 333 billion emails are sent daily, and that number is expected to grow to 376 billion by 2025. For most, emails are as simple as composing a message and clicking "send," but the process behind sending emails is much more complex. For example, transactional email templates show how specific user actions trigger automated communications.
The technical term for email is 'electronic mail,' which has a rich history in the development of networked messaging systems and the evolution of communication protocols.
Behind the scenes, there are multiple systems, servers, and protocols that help deliver your emails. A critical email protocol known as SMTP helps set everything in motion and is at the core of sending emails. SMTP can be thought of as a digital postal service, ensuring reliable delivery of your messages across the internet. SMTP operates over the transmission control protocol (TCP), which provides dependable message delivery between servers. Email services and smtp services are essential components of the email infrastructure, handling the transmission, protocols, and reliability of email delivery. What is an SMTP server, and how does it work? We define what it is, how it works and discuss the pros and cons of running an SMTP server on your own versus using a third-party service.
Defining Simple Mail Transfer Protocol (SMTP)
Simple Mail Transfer Protocol (SMTP) is a standard method for transferring information via email, also known as an “email protocol.” The SMTP protocol defines the rules for email transmission, specifying how email servers communicate and handle the transfer of messages. Email protocols are sets of rules used explicitly for sending email messages from one email account to another via the internet. Email protocols allow different email clients (Gmail, Outlook, Yahoo, etc.) and email accounts to exchange information easily.
SMTP is one of the most common email protocols and is the only dedicated protocol for sending emails. Email clients rely on SMTP to push messages from a sender account to a receiving account. Mail clients use standardized SMTP commands to communicate with servers, initiate connections, authenticate, and route messages.
Proper configuration of SMTP settings and the use of correct SMTP ports are essential for successful and secure email delivery.
What Is an SMTP Server?
Now that we’ve defined what Simple Mail Transfer Protocol (SMTP) is, we can discuss SMTP servers. A server is software that provides a service to other computer applications within a network. An SMTP server sends, receives, and relays email messages using the internet to transfer information from one server to another. An smtp email server often acts as the outgoing mail server responsible for sending emails.
SMTP servers act as the delivery tool that processes and sends emails from one destination to another. SMTP servers can deliver single, transactional, and bulk emails securely within minutes. The email transmission process is initiated by a mail user agent (MUA), which is the client software used by end users to compose and send emails. The MUA acts as an smtp client, and smtp clients establish connections with the smtp email server to begin the sending process. Mail submission agents and mail transfer agents (also known as message transfer agents or mail agents) work together to relay and deliver emails through the SMTP infrastructure.
How Does SMTP Work?
SMTP can be a complex protocol, but we’ll explain the technical rules, commands, and sending processes without getting too granular.
SMTP servers are used over common email providers because SMTP are dedicated servers that allow scaling. The first step is to set up the SMTP server, which will enable email clients like Gmail, Outlook, or Apple Mail to communicate with your server. The SMTP session begins when the client sends the HELO command to the server to initiate communication. With the communication stream open, you are now ready to send emails.
Once you’ve sent an email, the email client will open an SMTP connection to your server. The sender SMTP (the SMTP client) establishes a TCP connection with the server and uses the SMTP envelope to specify the sender's email address and recipient's email address. The SMTP server uses the internet to locate and talk to a domain name server (DNS). The DNS will provide the server information to help the email reach the right recipient. The server performs a mail exchange lookup to identify the recipient's domain and locate the recipient's mail server or recipient's SMTP server. The server and the DNS work together to locate information, or Mail Exchanger (MX) records such as the sender’s email address, the recipient’s email address, and the email’s content.
If the sender and receiver’s domains are the same, the email will be sent instantly. If the domains differ, (for example, you’re sending an email from a Gmail account to an Outlook account), the DNS will need to identify the recipient’s domain to ensure it is sent to the correct server. Once this information is shared with the recipient server, that server will take over to complete the delivery and send the message to the recipient’s inbox. The receiving SMTP server (or receiving server) accepts the message and passes it to a mail delivery agent, which delivers it to the recipient's inbox.
Errors can occur when email domains and accounts change, or when other technical issues arise. Emails may bounce, be blocked, or get reported as spam, or technical issues between servers can occur. Internet service providers may block certain SMTP ports to prevent spam, and SMTP AUTH and the SMTP AUTH extension are used to authenticate users and prevent unauthorized relaying. SMTP relay and SMTP relay service are used to route emails through other SMTP servers to ensure successful message transfer across different domains. This is why it is essential to have an IT team to help with technical issues and why marketing teams should always scrub and “clean” email lists to help prevent errors and bounces.
In the context of outgoing emails, the SMTP service or SMTP email service acts as a mail carrier, ensuring reliable delivery of outgoing email messages. Overall, SMTP works by coordinating all these components and processes for successful email delivery.
SMTP Security Measures
As email remains a primary channel for business and personal communication, securing your SMTP server is more important than ever. Without proper security measures, SMTP servers can become targets for unauthorized access, spam, and phishing attacks, putting sensitive information and your reputation at risk.
One of the foundational elements of SMTP security is authentication. SMTP authentication ensures that only authorized users can send emails through your mail server, helping to prevent spammers from abusing your system. Common authentication methods include LOGIN, PLAIN, and CRAM-MD5, which require users to verify their identity before the SMTP server will process outgoing mail. By enabling SMTP authentication, you add a critical layer of protection to your email delivery process.
Encryption is another essential security measure for SMTP servers. By configuring your mail server to use Transport Layer Security (TLS) or Secure Sockets Layer (SSL) encryption, you protect email messages as they travel across the internet. This means that even if someone intercepts the data during transmission, the contents of your email remain secure and unreadable. Most reputable email service providers and SMTP providers offer SSL encryption as a standard feature, ensuring that your email communication is protected from eavesdropping.
Multipurpose Internet Mail Extensions (MIME) allow email clients to send and receive rich content, such as attachments and multimedia. While MIME enhances the functionality of email messages, it can also be exploited to deliver malicious files. To counter this risk, SMTP servers and mail servers should implement robust virus scanning and spam filtering. These tools help detect and block harmful attachments and unwanted messages before they reach the recipient’s inbox, safeguarding both your users and your network.
The roles of mail transfer agents (MTAs) and mail delivery agents (MDAs) are also crucial in maintaining SMTP security. MTAs handle the routing of emails between SMTP servers, while MDAs are responsible for delivering messages to the recipient’s inbox. Both must be configured to use secure protocols and strong authentication methods to prevent unauthorized access and ensure the integrity of your email delivery.
While SMTP is the protocol for sending emails, retrieving messages from a mail server is handled by Internet Message Access Protocol (IMAP) and Post Office Protocol (POP). IMAP allows users to access their email from multiple devices, while POP downloads messages to a single device. Both protocols should be secured with encryption and strong authentication to protect incoming messages and user credentials.
To maximize email security, it’s important to choose an email service provider that prioritizes SMTP security. Look for providers that offer features like SMTP authentication, TLS encryption, spam filtering, and delivery status notifications. These measures not only protect your outgoing emails but also help you track the status of your email delivery, making it easier to identify and resolve potential issues.
End users can also contribute to secure email communication by using strong, unique passwords for their email clients, keeping their software up to date, and exercising caution when opening attachments or clicking links from unknown senders.
In summary, SMTP security is a vital component of safe and reliable email delivery. By combining proper server configuration, strong authentication, robust encryption, and vigilant user practices, both organizations and individuals can protect their email messages and maintain the integrity of their digital communication.
Running an SMTP Server — Use Your Own or a Third-Party Service?
Now that you're ready to run an SMTP server, the big question is, do you use your own, or a third-party service? There's no “right” answer. It truly depends on your needs and the resources you have. Let's start by looking at what it would take to run your own SMTP server.
Running Your Own SMTP Server
Running your own SMTP server can have many benefits, such as no sending limits. Some third-party providers will put caps or limitations on how many emails you can send per day, week, month, etc. With a dedicated SMTP, you can send all the emails you want. Another significant aspect of having your own server is having full access to monitor all delivery information. This can help you discover error codes and help you improve your email methodology. You also remain in complete control of your email lists, which is important for preserving private data from your company and your customers.
Though there are many benefits to running your own SMTP server, you should first consider whether or not you have the resources to accommodate it. Not only will you need someone knowledgeable to set it up, but SMTP servers need to be monitored regularly. For example, you'll likely need a dedicated team to monitor and maintain the server, which can be costly.
Another thing to consider is that running your own SMTP server will require it to be local. When you have a local server, it can be vulnerable to power and connectivity issues in your area. You'll need backup servers and other failsafe protections in place, plus a staff member with technical knowledge to fix things when they do fail.
Lastly, deliverability and security issues can arise. Even with a great team, there are still challenges preventing spammers from accessing your server. You'll need to have protection plans and processes in place to detect unauthorized spam and adjust strategies as needed. However, if you have the resources to set up and maintain your own SMTP server, the benefits could make this a good option for you.
Using a Third-Party Email Service
Hiring a third-party email service can be an excellent option for companies that don't have the staff resources or just don't want to deal with the hassle of running their own SMTP server. Whatever company you choose will typically take care of the setup, monitoring, and maintenance of your email server. The plus side is that these services already have expert teams for technical support, security, and failsafe plans.
Third-party companies often have high security and IT support standards already wrapped into the service. You shouldn't have to worry about additional costs, as most services are billed at a fixed rate. Lastly, these companies excel in emails. They know the ins and outs of ISPs and mailbox providers to ensure reliable deliverability. They have their processes figured out and know what works, so there's no time wasted with trial and error.
Hiring a third-party email service can be less hassle and more secure, cost-effective, and reliable. However, a drawback for some is that you're not in complete control. You have to rely on others to alert you of issues, relay information, and trust that they're using the best practices. Not only that, but you also have to share information about your company and share your customer's data (email lists) with them.
Dealing with their terms and conditions can also be a pitfall. As we mentioned above, sometimes providers have caps on how many emails you can send in a specific time frame. When hiring an email service provider, be sure to check for limitations and read reviews to find someone with superior customer support and domain expertise.
Conclusion
When it comes to marketing, advertising, and communication, email is still leading the race. If you want to send powerful and effective marketing or business emails, you'll need to utilize an SMTP server.
If you're interested in setting up your own SMTP server, make sure you have the resources to negate some potentially expensive challenges. A lack of resources or the expense of running their own SMTP server is the main reason many companies choose to use third-party providers. These services can design hassle-free email infrastructures for reliable and secure sending. If you're looking for a more robust way to notify your users about important information, promotions, and updates, open source notification systems provide flexibility and control for developers. MagicBell provides a notification inbox solution that developers can implement as a plug-and-play notification solution. Additionally, MagicBell's inbox system makes life easier for developers as it can be implemented in mere minutes.