#Mail_Server

Mail Server

Mail server. It is a computer application whose function is similar to postal mail only in this case it is electronic mail (sometimes called messages) that circulate, they do it through our data transmission networks and unlike postal mail, by this means only They can send attachments of files of any extension and not packages or packages when traveling the information in electronic format.

A server that allows me to exchange emails, whether between users, Servers, client, and server. This server stores and forwards the mail messages, this is probably the most used TCP / IP application.

Protocols

To carry out the operation of the mail server some protocols are necessary:

SMTP

SMTP, Simple Mail Transfer Protocol: Known as Transport Protocol, it is the protocol used to send mail either from one mail server to another or from an email client to [[server].

Mail delivery from a Client Application to a Server, and from a source server to the destination server is managed by the Simple Mail Transfer Protocol (SMTP). The main purpose of the Simple Mail Transfer Protocol, SMTP, is to transfer mail between Mail Servers. However, it is critical for mail clients.

In order to send mail, the client sends the message to an outgoing mail server, which contacts the destination mail server for delivery. For this reason, it is necessary to specify an SMTP server when configuring an email client. As long as we don't use web-based mail (Webmail).

An important point about the Simple Mail Transfer Protocol protocol is that it does not require authentication. This allows anyone on the Internet to send mail to any small or large group of people. This feature of SMTP is what makes spam or spam possible.

Servers that do not put such restrictions are called open relay servers. Mail access protocols.

POP protocol

POP, Post Office Protocol: It is used to obtain messages saved on the server and pass them on to the user.

When using the POP Protocol, email messages are downloaded through client email applications. By default, most POP mail clients are automatically configured to delete the message on the mail server after it has been successfully transferred, however, this setting can be changed.

To add security, it is possible to use Secure Socket Layer (SSL) encryption for client authentication and data transfer sessions.

POP3

The SMTP protocol is responsible for sending the mail and receiving it in the user's mailbox. Additional protocols, such as POP3, are used to access the mailbox remotely. POP3 is a protocol that allows access to a user's mailbox and performs the following operations:

Read the list of messages.

Read a message.

Delete a message.

Read the header of a message (only on some POP3 servers).

This protocol is very widespread on the Internet. Using the SMTP and POP3 protocols, a mail client program can remotely access a mail server and send and receive mail. Integration with the NT database This option is highly recommended since it avoids creating email accounts separately. This way you can easily add users to the mail server automatically.

IMAP 

IMAP, Internet Message Access Protocol: Its purpose is the same as that of POP, but the operation and functionalities they offer are different.

When using an IMAP mail server, mail messages are kept on the server where users can read and delete them. IMAP also allows client applications to create, rename, or delete directories on the server to organize and store mail. IMAP is mainly used by users who access their mail from multiple machines.

The protocol is also suitable for users who are connecting to the mail server through a slow connection, because only the information in the mail header is downloaded for the messages, until they are opened, thus saving bandwidth. The user also has the ability to delete messages without viewing or downloading them. For additional security, SSL encryption can be used for client authentication and for data transfer sessions.

Other free as well as commercial IMAP clients and mail servers are also available, many of which extend the IMAP protocol and provide additional functionality. Characteristics of mail servers When configuring an Internet mail server or an Intranet, this server should support a number of functions. The most important are: Support for the SMTP protocol: Virtually all mail on the Internet is managed using this protocol.

The SMTP is responsible for sending messages from one server to another. The messages are stored on the source servers until they can be transferred to the destination server, either directly, or through intermediate servers that act as gateways. The most used SMTP server is SendMail since it is distributed with all UNIX. This is the server that is taken as a reference to evaluate other SMTP servers.

Post office support: A post office is a server that is configured as an entry point in a domain. Its mission is to receive external mail and distribute it among the organization's different mail servers. You can also process outgoing mail, so that it conforms to a series of rules established in the domain, such as that all messages follow the same rules in usernames. Usually, in an organization, there is more than one post office.

Post offices are identified within the DNS name service with the MX key fields. Estafetas normally receive the mail that is sent to the domain, that is, the mail that is sent to the users. Estafetas normally distribute mail using alias lists.

Alias   List Support: A mail server must support aliases, or synonyms of a username. Normally an alias list is a file that contains pairs of names: an alias and the account to which the mail should be redirected.

Main server programs

These are used on the mail server computer to provide the service to customers, who can use it through a mail program

Mercury Mail Server: Windows, Unix, GNU / Linux.

Microsoft Exchange Server: Windows.

MailEnable: Windows.

Exim: Unix.

Sendmail: Unix.

Qmail: Unix.

Postfix: Unix.

Zimbra: Unix, Windows.

Lotus Domino: GNU / Linux, OS400, Windows.