Email client

An email client (alternatively spelled e-mail client; commonly known as mail client; more formally known as mail user agent or MUA; hereinafter, the Client) is any digital construct that an end-user utilizes to compose, access, and/or manage his or her emails.

The Client can also refer to mail client software. More broadly, email software may refer to all the software utilized for the Clients, mail servers, or mail exchangers.

Functions

Communication

With regard to:

• Outgoing messages, the Clients may be designed to:
  1. Accept requests from end-users to compose new messages.
  2. Analyze requests looking for their inconsistencies and/or missing data.
  3. Offer end-users to correct inconsistencies and/or add the missing data.
  4. Transfer messages to mail servers.
• Stored messages, the Clients may be designed to:
  1. Accept requests from end-users to manage -- delete, arrange, label, classify -- stored messages.
  2. Offer end-users to confirm those changes that are setup as critical.
  3. Execute the requests -- delete, arrange, label, classify -- stored messages.
• Incoming messages, the Clients may be designed to:
  1. Accept messages from mail servers.
  2. Analyze messages looking for their inconsistencies and/or missing data.
  3. Add information about the found inconsistencies and/or missing data to the messages. This information may further be used by mail clients to combat spam.
  4. Display messages to end-users.

On the one side, the Clients receive requests from and display the data to end-users. On the other side, the Clients communicate with mail servers in order to receive emails from and/or send emails to.

Hosting

There are two major models of locating the Clients:

1. On-premises: end-users may install the Clients on their devices; a common example would be an app running on one's cell phone. The POP3 protocol is commonly used for sending one's emails to and/or receiving from mail servers.
2. Online: end-users may access the Clients that are hosted online, often, next to a mail server. The IMAP protocol is commonly used for accessing and/or managing one's emails online.

Software

General comparison

General comparison of the popular Clients

Category	Features	Evolution	Outlook	RoundCube	Thunderbird	Zimbra
Trivia	Ownership	OSS	Proprietary	OSS	OSS	OSS
	Developer	Community	Microsoft	Community	Foundation	Corporation
	License	GPL	Unknown	GPL	MPL	YPL-like
	UI	GUI (GTK+)	GUI	Webmail	GUI (XUL)	GUI
	Latest release	3.32.2	2019(16)	1.2.5	60.7.2	8.6.0
Date		05/08/2019	09/24/2018	04/28/2017	06/20/2019	12/15/2014
	Introduction	2000	1997	2006	2003	2005
OS	Windows	No	Yes	Cross-platform	Cross-platform	Cross-platform
	macOS	No	Yes
	Linux	UNIX-like	No
	BSD		No
	Unix		No

Communication protocols

Communication protocols supported by the popular Clients

Category	Features	Evolution	Outlook	RoundCube	Thunderbird	Zimbra
POP3	Fetch all messages	Yes	Yes	Yes	Yes	Yes
	Selected by filter	No	No	No	No	No
	Selected by user	Yes	No	No	No	No
Non-POP3 communication protocols	IMAP4
	SMTP
	NNTP
	EWS
	IPv6
	MAPI
RSS	0.91 Feeds
	1.0 Feeds
	2.0 Feeds
LDAP	v2
	v3
Non-RSS integration protocols	IMSP
	ACAP
	ATOM Feeds
	iCalendar
	MAPI/RPC
	CalDAV
	CardDAV
Regular authentication	Login
	Plain
CRAM-HMAC	MD5
	SHA1
	RIPEMD
	MD5 APOP
	DIGEST-MD5
Other authentication	MSN (NTLM) browser login
	Compuserve (RPA)
	Hardware token PKCS#11
	Biometric
	SMTP Auth
	X.509 client certificate
	OAuth
SSL/TLS support	Secure POP3
	Secure IMAP4
	Secure SMTP
	Secure NNTP
	Secure LDAP
	SNI
	OCSP
	CRL
Filtering	Local junk
	Server-side junk
	Phishing
PGP support	inline
	PGP/MIME or OpenPGP
S/MIME support	protocol
	OCSP
	CRL
	Certificates on tokens, smartcards support
Appearance	HTML email
	UTF-8 support
	Image blocking
	Thread view
	Conversation view
Message (general)	Bi-directional text support
	Postpone/scheduled message sending
Label messages	with colors
	with flag
	antidelete
	add note
Reformat received messages	edit headers (e.g., Subject)
	forced recode
Composing messages	Spell checking
	Signatures
	Bottom-posts replies
Native images preview	jpeg
	gif
	bmp
	png
	others
Native documents preview	txt
	pdf
	doc
	xls
	odt
	ods
	others
Database	Message file format
	Encrypted database
	Virtual folders
	Scheduled backup
New mail notification	ticker
	tray icon
	tooltip
	sound
Folders	Customizable interface
	Customizable keybindings
	Fragmented messages
	Database search with regular expressions support
	Indexed search
	Search folders
IMAP	Search
	IDLE
Message templates	new
	reply
	forward
	read
	confirmation
	save
	print
	Individual for
Support in message templates scripts, programming languages	JavaScript
	VBScript
	PHP Scripts
	Python
	Regular expressions
	Java
	Other (specify)

Related lectures

• Communication Quarter.