Email Clients Explained: Desktop vs Webmail

An email client is software that sends, receives, and manages email messages from one or more email accounts. This article defines what an email client does, separates desktop email clients from webmail services, explains the IMAP, POP3, and SMTP protocols that move messages between a client and a mail server, and compares the major email clients in use today. Desktop email clients such as Microsoft Outlook, Mozilla Thunderbird, and Apple Mail install on a computer and store mail locally, while webmail services such as Gmail and Outlook.com run inside a web browser.

The protocol an email client uses determines whether messages stay on the server or download to the device, and whether the same mailbox stays in sync across multiple devices. The sections below cover account protocols, core features such as a unified inbox and message filters, offline access, encryption support, and the difference between a locally installed program and a browser-based service. A comparison table sets desktop email clients against webmail across the attributes that separate the two categories.

What Is an Email Client?

An email client is a program that connects to a mail server to send, receive, organize, and store email messages. An email client communicates with a mail server through standard internet protocols and presents messages in folders such as Inbox, Sent, and Drafts. An email client falls into two categories by where the software runs.

• Desktop email clients install on a device. A desktop email client such as Microsoft Outlook or Mozilla Thunderbird runs as a local application and stores messages on the computer.
• Webmail services run in a browser. A webmail service such as Gmail or Outlook.com loads through a web address and stores messages on the provider servers.
• Mobile email apps run on phones. A mobile email app such as Apple Mail or Gmail for Android connects to the same mailbox through the same protocols.

An email client differs from a mail server. A mail server, such as Microsoft Exchange or a provider mail host, stores and routes messages, while the email client retrieves and displays those messages. Email software belongs to the wider category of productivity tools described in the guide to software applications.

How Does an Email Client Work?

An email client works by connecting to a mail server with login credentials, then using one protocol to fetch incoming mail and a second protocol to send outgoing mail. The mail client authenticates with a username and password, requests the message list, and transfers message content over an encrypted connection.

The transfer follows a fixed sequence each time the email client checks for mail.

1. Authenticate with the mail server. The email client sends the account username and password to the incoming mail server.
2. Retrieve the message list. The mail server returns message headers such as sender, subject, and date over IMAP or POP3.
3. Download message content. The email client downloads the message body and any attachments on demand or in full.
4. Send outgoing mail through SMTP. The email client hands new messages to the SMTP server, which routes them to the recipient mail server.

Encryption protects this exchange. Transport Layer Security wraps the connection between the email client and the mail server, which prevents a third party from reading login details or message content in transit.

What Are the Email Protocols (IMAP, POP3, SMTP)?

Email clients use three core protocols: IMAP and POP3 retrieve incoming mail, while SMTP sends outgoing mail. The retrieval protocol an email client uses decides whether messages stay on the server or move to the device.

• IMAP keeps mail on the server. Internet Message Access Protocol syncs folders and read status across every device, so the same mailbox state appears on a laptop, a phone, and a browser.
• POP3 downloads mail to one device. Post Office Protocol version 3 transfers messages to a single device and, by default, removes them from the server.
• SMTP sends outgoing mail. Simple Mail Transfer Protocol carries new messages from the email client to the mail server and on to the recipient.
• Exchange ActiveSync syncs corporate mail. Microsoft Exchange uses its own protocol to sync mail, calendar, and contacts for business accounts.

IMAP suits a mailbox used across several devices, since the server holds the authoritative copy. POP3 suits a single device with limited server storage, because messages move off the server after download. The Internet Engineering Task Force defines IMAP in RFC 3501 and SMTP in RFC 5321, which sets the standard behavior every email client follows.

What Are Desktop Email Clients?

A desktop email client is an application installed on a computer that stores and manages email locally. A desktop email client connects to one or more accounts and keeps a copy of messages on the device for fast search and offline reading.

Three desktop email clients hold the largest share of installed mail software.

• Microsoft Outlook combines mail with calendar. Outlook ships in the Microsoft 365 suite and connects to Exchange, IMAP, and POP3 accounts, with integrated calendar, contacts, and tasks.
• Mozilla Thunderbird is free and open source. Thunderbird, maintained by Mozilla, supports IMAP, POP3, and SMTP across Windows, macOS, and Linux at no cost.
• Apple Mail ships with macOS. Apple Mail is the built-in email client on macOS and iOS and connects to iCloud, Exchange, and standard IMAP accounts.

A desktop email client stores mail in a local database, which allows full-text search without a connection. The Microsoft Outlook program also forms part of the wider office package covered in the explanation of office suites.

What Is Webmail?

Webmail is an email service accessed through a web browser without installed software. Webmail loads the mailbox from the provider servers and displays messages inside a browser tab, which requires an active internet connection.

Two webmail services account for most browser-based email use.

• Gmail runs on Google servers. Gmail, from Google, offers search-based mail organization, conversation threading, and label filing through any modern browser.
• Outlook.com runs on Microsoft servers. Outlook.com provides browser-based mail tied to a Microsoft account, with a folder structure and integrated calendar.

Webmail stores messages on the provider servers, so any device with a browser reaches the same mailbox. A browser displays webmail without a separate program, a function described in the explanation of what a web browser is. The choice of browser affects webmail performance, a topic compared in the article on the best web browsers compared.

Desktop Email Client vs Webmail: What Is the Difference?

The difference between a desktop email client and webmail is where the software runs and where messages are stored. A desktop email client installs on the device and stores mail locally, while webmail runs in a browser and stores mail on provider servers. The table below compares the two categories across the attributes that separate them.

A desktop email client suits a mailbox that needs offline access and several accounts in one place. Webmail suits a mailbox reached from many devices without installing software.

What Features Do Email Clients Offer?

Email clients offer features that organize, filter, and secure mail beyond sending and receiving. The features below appear in most desktop email clients and webmail services, ordered by how often a mailbox relies on each one.

• A unified inbox combines accounts. A unified inbox merges mail from several accounts into one message list, which a desktop email client such as Thunderbird provides.
• Filters sort mail automatically. A filter applies a rule, such as moving messages from a sender into a folder, without manual sorting.
• Search finds messages by content. Full-text search locates a message by sender, subject, or body text across folders.
• Encryption protects message content. S/MIME and OpenPGP encrypt the message body so only the intended recipient reads it.
• Calendar and contacts integrate with mail. Microsoft Outlook and Apple Mail link mail to a calendar and address book in one program.
• Offline access reads downloaded mail. A desktop email client opens downloaded messages without a connection, which webmail cannot do by default.

Message encryption in an email client supports the same goal as file-level protection. The broader topic of encryption software covers how encryption secures data beyond email.

Key Takeaways

• An email client sends and receives mail. An email client connects to a mail server to manage messages in folders.
• Desktop clients store mail locally. Outlook, Thunderbird, and Apple Mail install on a device and read mail offline.
• Webmail runs in a browser. Gmail and Outlook.com store mail on servers and need an internet connection.
• IMAP syncs across devices. IMAP keeps mail on the server, while POP3 downloads mail to one device.
• SMTP sends outgoing mail. SMTP carries new messages from the client to the recipient mail server.
• Encryption secures mail in transit. TLS protects the connection, and S/MIME or OpenPGP encrypts message content.

Last Thoughts on Email Clients

An email client sends, receives, and manages mail by connecting to a mail server through IMAP, POP3, and SMTP. The choice between a desktop email client and webmail comes down to where the software runs and where messages are stored, since a desktop client such as Microsoft Outlook or Mozilla Thunderbird stores mail locally and reads it offline, while Gmail and Outlook.com keep mail on provider servers and load in a browser.

IMAP suits a mailbox used across many devices, and POP3 suits a single device with limited server storage. Email software sits within the wider set of software applications, alongside the office suites that bundle mail with documents and calendars.