How e-mail works: the invisible engine that keeps companies communicating

How does e-mail actually work?

For many people, e-mail “just works”. We write a message, choose the recipient, click send and it reaches its destination. However, behind this apparent simplicity there is a technical infrastructure made up of servers, e-mail clients, communication protocols and synchronisation processes that determine the reliability and performance of the service. This article explains, in a clear and accessible way, how e-mail works in practice.

A brief history: from academic tool to essential service

Electronic messaging emerged in the 1970s as a simple means of communication between researchers, quickly gaining relevance thanks to its efficiency. The well-known “@” symbol (“at”) was introduced in 1971 to separate the user and the server (domain) where the user’s mailbox is stored. In Portugal, e-mail began to expand in the early 1990s, first in the academic environment and shortly afterwards through the first commercial services. Despite the technological limitations of the time, e-mail quickly became the main form of professional communication and is now an essential element for any company.

The two fundamental components of e-mail

For today’s analysis, the operation of e-mail relies on two essential elements that work together:

• the E-mail Server
• the E-mail Client

The e-mail server is the central software responsible for receiving, storing and sending messages. The e-mail client is the application used by the user to access the server. Users interact with the e-mail service using an e-mail client.

The e-mail server

The e-mail server is the software that forms the core of the service. It is software hosted on a server, either on the customer’s premises or in the cloud, permanently connected to the internet, and responsible for managing the entire message flow of one or more organisations. In the case of the Yobi365 Connect service, the e-mail server used is Carbonio, developed by the company Zextras after more than 25 years of collaboration with the Zimbra platform.

Main functions of the server

• Receiving e-mails from the Internet.
• Storing all messages associated with the user’s account, i.e., the user’s mailbox.
• Delivering messages to e-mail clients.
• Delivering messages to other e-mail servers.

The server operates as an “intelligent central archive” where the actual information of the user’s mailbox resides and is processed.

How servers communicate with each other

When an e-mail is sent, the originating server “consults the Internet” to identify which server is responsible for the recipient’s domain and forwards the message through the SMTP protocol — Simple Mail Transfer Protocol. As with traditional mail, the message may pass through several systems before reaching its destination. If the remote server is temporarily unavailable, the message remains queued and new attempts are made until delivery becomes possible or the message is returned, ensuring that nothing is lost and that the process resumes as soon as the service is restored.

The e-mail client

The e-mail client is the application that allows the user to write and send messages, receive and read messages and organise their mailbox. Although each e-mail client has its own design and more or fewer features, all implement the basic functionalities: receiving, reading, writing, sending and managing messages and folders.

E-mail access can be done in two main ways. With web access, the user opens e-mail directly in the browser without installing additional software, always working with the most up-to-date version of the mailbox stored on the server. With a locally installed application — the traditional e-mail client — the user works with dedicated software offering its own features and integrating e-mail into the desktop environment. To these two models we add access via mobile applications, now essential for mobility.

Common examples include:
• Web access: connect.yobi365.com or Google’s webmail at mail.google.com
• Local applications: Outlook, Thunderbird, Apple Mail
• Mobile applications: Gmail, Apple Mail, TypeApp, BlueMail, Spark, among others

How the client communicates with the server: protocols and security

For the client and server to exchange information, protocols are used that define how messages are transferred and synchronised. While all can operate with encrypted connections to ensure security (highly recommended), they differ in how they manage mailbox content.

POP3 was designed to download messages to a single device, often deleting them from the server. This model makes working with multiple devices difficult and increases the risk of data loss.
IMAP is currently the recommended standard. It keeps all messages on the server, synchronises folders and message status in real time, and guarantees full consistency across devices — a fundamental requirement in modern business environments.
ActiveSync offers a higher level of integration, synchronising not only e-mails but also contacts, calendars and other essential productivity information.

Overall, POP3 is now inadequate for the professional context, while IMAP and ActiveSync ensure greater security, robustness and a consistent experience across all devices.

In practice, how e-mail works

The process is simple: the user writes a message in the e-mail client, which sends it to the organisation’s e-mail server. The server forwards the e-mail to the recipient and stores a copy in the sender’s account. From that moment on, all devices associated with that account automatically synchronise the message, ensuring the mailbox shows the same state on any device.

The same happens with every user action. When deleting, moving, archiving or marking a message as read, the server records the change and replicates the update across all devices. This centralised model guarantees reliability, organisation and a uniform experience regardless of where the e-mail is accessed.

Modern challenges: security, large-scale communication and data protection

Despite the maturity of the technology, e-mail continues to face significant challenges that directly impact the operation and reputation of companies. Among the most relevant are spam, malware, phishing attempts and blacklisting issues, which can compromise message delivery and require strong authentication and filtering mechanisms. These topics — essential for any organisation — will be explored in a dedicated article on e-mail security and reliability.

Another critical aspect is the sending of large-scale communications. Newsletters and informational campaigns follow specific rules and rely on deliverability processes, consent management and domain reputation. As these sendings should not be handled in the same way as daily e-mail, we will soon cover best practices and the most suitable tools for large-scale communication.

Finally, the use of e-mail in a corporate context is directly related to GDPR compliance. The way messages and personal data are stored, accessed, archived and shared involves clear legal responsibilities for organisations. This topic will be developed in a forthcoming article focusing on the legal framework and best practices for data protection applied to e-mail.

The role of Yobi365 Connect

To ensure a stable, secure e-mail service aligned with everyday business needs, Yobi365 Connect offers a dedicated solution with specialised support, full control over organisational data and robust security practices. The platform combines reliability, ease of use and continuous system management, supported by the know-how of the Yobi365 teams, enabling companies to remain focused on what matters most: their business.