E-mail client - Citizendia

An e-mail client, aka Mail User Agent (MUA), aka email reader is a frontend computer program used to manage email. Mozilla Thunderbird is a free, Open source, Cross-platform e-mail and News client developed by the Mozilla Foundation. Computer programs (also software programs, or just programs) are instructions for a Computer. Electronic mail, often abbreviated to e-mail, email, or originally eMail, is a Store-and-forward method of writing sending receiving

Sometimes, the term e-mail client is also used to refer to any agent acting as a client toward an e-mail server, independently of it being a real MUA, a relaying server, or a human typing directly on a telnet terminal. A mail transfer agent (MTA (also called a mail transport agent, message transfer agent, or smtpd (short for SMTP daemon) is a In addition, a web application providing the relevant functionality is sometimes considered an email client.

1 Functionality and configuration of a MUA
2 Encryption
- 2.1 Encryption of mail sessions
- 2.2 Encryption of the message body
3 Standards
- 3.1 Port numbers
4 Webmail
5 See also

Functionality and configuration of a MUA

Although mail user agents aim at enabling users to deal with their mail with minimal technical knowledge, some understanding of the operations involved is useful for making savvy configuration decisions.

Retrieving messages from a mailbox

Like most client programs, a MUA is only active when a user runs it. Messages arrive on the Mail Transfer Agent (MTA) server. A mail transfer agent (MTA (also called a mail transport agent, message transfer agent, or smtpd (short for SMTP daemon) is a Unless the MUA has access to the server's disk, messages are stored on a remote server and the MUA has to request them on behalf of the user.

In the first case, shared disk, a user logs on a server and runs a MUA on that machine. The MUA reads messages from a conventionally formatted storage, typically mbox, within the user's HOME directory. mbox is a generic term for a family of related File formats used for holding collections of electronic mail messages The MTA uses a suitable Mail Delivery Agent (MDA) to add messages to that storage, possibly in concurrence with the MUA. A Mail Delivery Agent ( MDA) is Software that delivers E-mail messages right after they've been accepted on a server distributing them to recipients' individual This is the default setting on many Unix systems. Webmail applications running on the relevant server can also benefit from direct disk access to the mail storage.

For personal computing, and whenever messages are stored on a remote system, a mail user agent connects to a remote mailbox to retrieve messages. An Email mailbox is the email equivalent of a Letter box, it is where email messages are delivered Access to remote mailboxes comes in two flavors. On the one hand, the Post Office Protocol (POP) allows the client to download messages one at a time and only delete them from the server after they have been successfully saved on local storage. In Computing, local E-mail clients use the Post Office Protocol version 3 ( POP3) an application-layer Internet standard protocol It is possible to leave messages on the server in order to let another client download them. However, there is no provision for flagging a specific message as seen, answered, or forwarded, thus POP is not convenient for users who access the same mail from different machines or clients. On the other hand, the Internet Message Access Protocol (IMAP) allows users to keep messages on the server, flagging them as appropriate. The Internet Message Access Protocol or IMAP is one of the two most prevalent Internet standard protocols for E-mail retrieval the other being POP3 IMAP provides sub-folders. Typically, the Sent, Drafts, and Trash folders are created by default.

Both POP and IMAP clients can be configured to access more mailboxes at the same time, as well as to check each mailbox every given number of minutes. IMAP features an idle extension for real time updates, that may work better than polling when long lasting connections are feasible.

Client settings require the server's name or IP address, and the user name and password for each remote incoming mail box.

Formatting messages

Mail user agents usually have built-in the ability to display and edit text. Editing HTML text is a popular feature. HTML, an initialism of HyperText Markup Language, is the predominant Markup language for Web pages It provides a means to describe the structure Invoking an external editor may be an alternative.

MUAs responsibilities include proper formatting according to RFC 2822 for headers and body, and MIME for non-textual content and attachments. Electronic mail, often abbreviated to e-mail, email, or originally eMail, is a Store-and-forward method of writing sending receiving Electronic mail, often abbreviated to e-mail, email, or originally eMail, is a Store-and-forward method of writing sending receiving Multipurpose Internet Mail Extensions ( MIME) is an Internet standard that extends the format of e-mail to support text in Character Headers include the destination fields, To, Cc, and Bcc, and the originator fields From which is the message's author(s), Sender in case there are more authors, and Reply-To in case responses should be addressed to a different mailbox. To better assist the user with destination fields, many clients maintain one or more address books and/or are able to connect to an LDAP directory server. The Lightweight Directory Access Protocol, or LDAP (ˈɛl dæp is an Application protocol for querying and modifying Directory services running over For originator fields, clients may support different identities.

Client settings require the user's real name and email address for each user's identity, and possibly a list of LDAP servers.

Submitting messages to a server

As a basic function, a MUA is able to introduce new messages in the transport system. Typically, it does so by connecting to either an MSA or an MTA, two variations of the SMTP protocol. A mail submission agent or A mail transfer agent (MTA (also called a mail transport agent, message transfer agent, or smtpd (short for SMTP daemon) is a Simple Mail Transfer Protocol ( SMTP) is a De facto standard for electronic mail (e-mail transmissions across the Internet. The client needs to quickly put a message without worrying about where the message will be eventually delivered: that's why a transport system exists. Thus it always connects to the same preferred server. However, how does that server know that it should accept and relay submissions from that client? There are two ways. The older method recognizes the client's IP address, e. g. because the client is on the same machine and uses internal address 127. 0. 0. 1, or because the client's IP address is controlled by the same internet service provider that provides both internet access and mail services. An Internet service provider ( ISP, also called Internet access provider or IAP) is a company which primarily offers their customers access to the Internet The newer method, since the SMTP protocol has an authentication extension, is to authenticate. The latter method eases modularity and nomadic computing.

Client settings require the name or IP address of the preferred outgoing mail server, the port number (25 for MTA, 587 for MSA), and the user name and password for the authentication, if any. There is a non-standard port 465 for SSL encrypted SMTP sessions, that many clients and servers support for backward compatibility. Transport Layer Security ( TLS) and its predecessor Secure Sockets Layer ( SSL) are Cryptographic protocols that provide secure Transport Layer Security encryption can be configured for the standard ports, if both the client and the server support it. Transport Layer Security ( TLS) and its predecessor Secure Sockets Layer ( SSL) are Cryptographic protocols that provide secure

Encryption

With no encryption, much like for postcards, email activity is plainly visible by any occasional eavesdropper. E-mail encryption enables to safeguard privacy by encrypting the mail sessions, the body of the message, or both. E-mail encryption refers to Encryption, and often Authentication, of E-mail messages

Encryption of mail sessions

All relevant email protocols have an option to encrypt the whole session. Remarkably, those options prevent a user's name and password from being sniffed, therefore they are recommended for nomadic users and whenever the internet access provider is not trusted. An Internet service provider ( ISP, also called Internet access provider or IAP) is a company which primarily offers their customers access to the Internet On sending mail, users can only control encryption at the hop from a client to its configured outgoing mail server. At any further hop, messages may be transmitted with or without encryption, depending solely on the general configuration of the transmitting server and the capabilities of the receiving one.

Encrypted mail sessions deliver messages in their original format, i. e. plain text or encrypted body, on a user's local mailbox and on the destination server's. The latter server is operated by an email hosting service provider, possibly a different entity than the internet access provider currently at hand. An email hosting service is an Internet hosting service that runs Email servers

Encryption of the message body

There are two models for managing cryptographic keys. S/MIME employs a model based on a trusted certificate authority (CA) that signs users' public keys. S/MIME ( Secure / Multipurpose Internet Mail Extensions) is a standard for Public key Encryption and signing of E-mail encapsulated In Cryptography, a certificate authority or certification authority ( CA) is an entity which issues digital certificates for use by other parties OpenPGP employs a somewhat more flexible web of trust mechanism that allows users to sign one another's public keys. Pretty Good Privacy (PGP is a Computer program that provides Cryptographic Privacy and Authentication. OpenPGP is also more flexible in the format of the messages, in that it still supports plain message encryption and signing as they used to work before MIME standardization. Multipurpose Internet Mail Extensions ( MIME) is an Internet standard that extends the format of e-mail to support text in Character

In both cases, only the message body is encrypted. Headers, including originator, recipients, and subject, remain in plain text.

Standards

While popular protocols for retrieving mail include POP3 and IMAP4, sending mail is usually done using the SMTP protocol. In Computing, local E-mail clients use the Post Office Protocol version 3 ( POP3) an application-layer Internet standard protocol The Internet Message Access Protocol or IMAP is one of the two most prevalent Internet standard protocols for E-mail retrieval the other being POP3 Simple Mail Transfer Protocol ( SMTP) is a De facto standard for electronic mail (e-mail transmissions across the Internet.

Another important standard supported by most e-mail clients is MIME, which is used to send binary file e-mail attachments. Multipurpose Internet Mail Extensions ( MIME) is an Internet standard that extends the format of e-mail to support text in Character An e-mail attachment (or email attachment) is a Computer file which is sent along with an e-mail Attachments are files that are not part of the e-mail proper, but are sent with the e-mail.

Most e-mail clients use an X-Mailer header to identify the software used to send the message. In Information technology, header refers to supplemental Data placed at the beginning of a block of data being stored or transmitted According to RFC 2076, this is a common but non-standard header.

RFC 4409, Message Submission for Mail, details the role of the Mail submission agent. A mail submission agent or

RFC 5068, Email Submission Operations: Access and Accountability Requirements, provides a survey of the concepts of MTA, MSA, MDA, and MUA. It mentions that "Access Providers MUST NOT block users from accessing the external Internet using the SUBMISSION port 587" and that "MUAs SHOULD use the SUBMISSION port for message submission. "

Port numbers

TCP port numbers for email default as follows:

protocol	use	plain text or encrypt sessions	plain text sessions only	encrypt sessions only
POP3	incoming mail	110		995
IMAP4	incoming mail	143		993
SMTP	outgoing mail	25		(unofficial) 465
MSA	outgoing mail	587
HTTP	webmail		80	443

Webmail

In addition to the fat client e-mail clients and small MUAs, there are also Web-based e-mail programs called webmail. The Transmission Control Protocol ( TCP) and the User Datagram Protocol ( UDP) are Transport Layer protocols of the Internet Protocol In Computing, local E-mail clients use the Post Office Protocol version 3 ( POP3) an application-layer Internet standard protocol The Internet Message Access Protocol or IMAP is one of the two most prevalent Internet standard protocols for E-mail retrieval the other being POP3 Simple Mail Transfer Protocol ( SMTP) is a De facto standard for electronic mail (e-mail transmissions across the Internet. A mail submission agent or Hypertext Transfer Protocol ( HTTP) is a Communications protocol for the transfer of information on the Internet. A fat client or rich client is a computer ( client) in Client-server architecture networks which typically provides rich functionality independently The World Wide Web (commonly shortened to the Web) is a system of interlinked Hypertext documents accessed via the Internet. Webmail has several advantages which include the ability to send and receive e-mail from anywhere using a single application: a web browser. This eliminates the need to configure an email client. Significant examples of e-mail services which also provide the user a webmail interface are Hotmail, Gmail and Yahoo. Windows Live Hotmail, formerly known as MSN Hotmail and commonly referred to simply as Hotmail, is a free Webmail service of the Windows Live Gmail, officially Google Mail in Germany and the United Kingdom is a free POP3 and IMAP Yahoo! Mail is a Web-based email (webmail service from Yahoo!. The main drawbacks of webmail are that user interactions are subject to network response and that there is no offline capability. For instance, while webmail generally provides the best experience over broadband, a fat client can provide a satisfactory experience over dialup, and messages can be searched and viewed without an internet connection.

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