Correo electrónico

El módulo de correo electrónico se divide en tres partes principales:

  • Servidor SMTP para enviar y recibir 1

  • Servidor IMAP y POP3 para leer el correo electrónico 2, y el lenguaje Sieve para organizarlo 3

  • Antispam filter, antivirus and attachments blocker 4

Los beneficios son

  • autonomía completa en la gestión del correo electrónico

  • evitar problemas por el Proveedor de Servicios de Internet

  • capacidad de seguimiento de la ruta de los mensajes con el fin de detectar errores

  • optimized antivirus and antispam scan

Consulte también los siguientes temas relacionados:

  • Cómo funciona el correo electrónico 5

  • Registro MX DNS 6

  • Simple Mail Transfer Protocol (SMTP) 7

  • DKIM signature 8

Nota

Since NethServer 7.5.1804 new Correo electrónico, Connectors and POP3 proxy installations are based on the Rspamd filter engine. Previous NethServer installations are automatically upgraded to Rspamd as described in Email module transition to Rspamd

Dominios

NethServer can handle an unlimited number of mail domains, configurable from the Email > Domains page. For each domain there are two alternatives:

  • Deliver messages to local mailboxes, according to the Maildir 9 format

  • Relay messages to another mail server

Nota

Si se elimina un dominio, el correo electrónico no se eliminará; Se conserva cualquier mensaje recibido.

NethServer allows storing an hidden copy of all messages directed to a particular domain: they will be delivered to the final recipient and also to a custom email address. The hidden copy is enabled by the Copy inbound messages switch (formerly Always send a copy (Bcc) check box).

Advertencia

On some countries, enabling the Copy inbound messages switch can be against privacy laws.

Si no se puede establecer el destinatario final (p.e. si en destinatario no existe), el mensaje normalmente se rechaza. A veces (p.e. cuando migramos un dominio de correo), enviar el mensaje a un buzón general puede ser útil. Este comportamiento se puede lograr mediante :guilabel: aceptar la opción de destinatarios desconocidos.

DKIM signature

DomainKeys Identified Mail (DKIM) 8 provides a way to validate the sending MTA, which adds a cryptographic signature to the outbound message MIME headers.

To enable the DKIM signature for a mail domain, enable the Signature switch under Email > Domains > [list item] > Configure DKIM.

The DKIM signature headers are added only to messages sent through TCP ports 587 (submission) and 465 (smtps).

To work effectively, the public DNS must be configured properly. Refer to the instructions of your DNS provider to run the following steps:

  1. Add a TXT record to your public DNS service provider with key «default._domainKey»

  2. Copy and paste the given key text in the DNS record data (RDATA) section

Filtro

Todos los mensajes de correo electrónico en tránsito están sujetos a una lista de comprobaciones que se pueden activar selectivamente en la página: Correo electrónico > Filtro

  • Attachments

  • Antivirus

  • Antispam

Attachments

El sistema puede inspeccionar los archivos adjuntos de correo, denegando el acceso a mensajes que contengan formatos de archivo prohibidos. El servidor puede comprobar las siguientes clases de datos adjuntos:

  • ejecutables (eg. exe, msi)

  • archives (eg. zip, tar.gz, docx)

  • Lista de formato de archivo personalizado

The system recognizes file types by looking at their contents, regardless of the file attachment name. Therefore it is possible that MS Word file (docx) and OpenOffice (odt) are blocked because they actually are also zip archives.

Antivirus

The antivirus component finds email messages containing viruses. Infected messages are discarded. The virus signature database is updated periodically.

Antispam

The antispam component 4 analyzes emails by detecting and classifying spam 15 messages using heuristic criteria, predetermined rules and statistical evaluations on the content of messages.

The filter can also check if sender server is listed in one or more blacklists (DNSBL 14). A score is associated to each rule.

Total spam score collected at the end of the analysis allows the server to decide what to do with a message, according to three thresholds that can be adjusted under Email > Filter > Anti spam.

  1. If the spam score is above Greylist threshold the message is temporarily rejected. The greylisting 16 technique assumes that a spammer is in hurry and is likely to give up, whilst a SMTP-compliant MTA will attempt to deliver the deferred message again.

  2. If the spam score is above Spam flag threshold the message is marked as spam by adding the special header X-Spam: Yes for specific treatments, then it is delivered like other messages. As an alternative, the Add a prefix to spam messages subject option makes the spam flag visible on the subject of the message, by prefixing the given string to the Subject header.

  3. If the spam score is above Deny message spam threshold the message is rejected.

Los filtros estadísticos, llamados Bayesian 17, son reglas especiales que evolucionan y se adaptan rápidamente al análisis de mensajes marcados como spam o ham.

The statistical filters can then be trained with any IMAP client by simply moving a message in and out of the Junk folder. As a prerequisite, the Junk folder must be enabled from the Email > Mailboxes [General settings] > Configure [Advanced options] > Move spam to «Junk» folder check box (formerly Email > Mailboxes > Move to «Junk» folder» check box).

  • Al poner un mensaje en la carpeta de correo basura, los filtros aprenden que es spam y asignará una puntuación más alta a mensajes similares.

  • Por el contrario, al sacar un mensaje de la carpeta de correo basura, los filtros aprenden que este es ham: la próxima vez se le asignará una puntuación menor.

By default, all users can train the filters using this technique. If a group called spamtrainers exists, only users in this group will be allowed to train the filters.

El ajuste del filtro bayesian se aplica a todos los usuarios del sistema, no solo al usuario que marcó un correo electrónico como spam o ham.

Es importante entender cómo funcionan realmente las pruebas Bayesian:

  • No marca específicamente los mensajes como spam si contienen un asunto específico o la dirección del remitente. Solo está recopilando características específicas del mensaje.

  • Un mensaje solo puede marcarse una vez. Si el mismo mensaje se marca varias veces, no afectará nada ya que las pruebas dinámicas ya han sido ajustadas por ese mensaje.

  • The Bayesian filter is not active until it has received enough information. This includes a minimum of 200 spams AND 200 hams (false positives).

    As the system receives that information, the progress of bayesian filter training can be monitored from the Email > Filter [Statistics] > Bayes training progress bar.

Nota

It is a good habit to frequently check the Junk folder in order not to lose email wrongly recognized as spam.

Rules for white and black lists

Si el sistema no reconoce el spam correctamente incluso después del entrenamiento, las listas blancas y listas negras pueden ayudar. Esas son listas de direcciones de correo electrónico o dominios respectivamente siempre permitidos y siempre bloqueados para enviar o recibir mensajes.

The section Email > Filter [Rules] > Details (formerly Rules by mail address) allows creating three types of rules:

  • Permitir de: se acepta cualquier mensaje del remitente especificado

  • Permitir a: se acepta cualquier mensaje al destinatario especificado

  • Bloquear de: cualquier mensaje del remitente especificado está bloqueado

The Allow rules have higher precedence over the Block ones. As soon as an Allow rule matches, the antispam and antivirus checks are skipped, the Block rule is not evaluated and the message is accepted.

Advertencia

Antivirus and antispam checks are skipped if an Allow rule matches

It is possible to create an Allow or Block rule even for an entire domain, not just for a single email address: you just need to specify the domain name (e.g. dev.nethserver.org).

When a second level domain domain name is specified it matches also its subdomains. For instance nethserver.org matches nethserver.org itself, dev.nethserver.org, demo.nethserver.org and so on.

Rspamd web interface

The antispam component is implemented by Rspamd 4 which provides its administrative web interface at

https://<HOST_IP>:980/rspamd

For more information on Rspamd, please read the Rspamd page.

Quarantine (beta)

NethServer scans all incomaing email messages before they are delivered to the user mailbox. The messages that are identified as spam will be sent to a specific user mailbox. The purpose of this feature is to verify the email before deleting it. If enabled, a mail notification is also sent to the postmaster (root alias) for each quarantined email.

Nota

The quarantined messages can be accessed using a web mail or an IMAP account

Advertencia

The mailbox used for quarantine, must be able to accept spam. It should be a local shared mailbox or a user mailbox. If an external account is used, make sure the account exists on the remote server. Please make sure the quarantine mailbox has been created only for this specific purpose, otherwise the mailbox will be overloaded with unwanted spam.

Quarantine is provided by an optional RPM named nethserver-mail-quarantine. Once it has been installed from the terminal you must manually set its database properties.

The properties are under the rspamd key (configuration database):

rspamd=service
...
QuarantineAccount=spam@domain.org
QuarantineStatus=enabled
SpamNotificationStatus=disabled

  • QuarantineAccount: The user or the shared mailbox where to send all spam messages (spam check is automatically disabled on this account). You must create it manually. You could send it to an external mailbox but then make sure to disable the spam check on the remote server

  • QuarantineStatus: Enable the quarantine, spam are no more rejected: enabled/disabled. Disabled by default

  • SpamNotificationStatus: Enable the email notification when email are quarantined: enabled/disabled. Disabled by default

For example, the following commands enable the quarantine and the mail notification to root:

config setprop rspamd QuarantineAccount spam@domain.org QuarantineStatus enabled SpamNotificationStatus enabled
signal-event nethserver-mail-quarantine-save

Mailboxes

Each user has a personal mailbox and any user name in the form <username>@<domain> is also a valid email address to deliver messages into it.

The list of mailboxes is shown by the Email > Mailboxes page. There are three types of mailboxes: Users, Groups and Public mailboxes.

Users mailboxes

The Edit button allows disabling the Access to email services (IMAP, POP3, SMTP/AUTH) for a specific user. Messages delivered to that user’s mailbox can be forwarded to multiple external email addresses.

Advertencia

Si el sistema está enlazado a proveedor de cuenta remota y una cuenta de usuario se elimina remotamente, el buzón asociado debe borrarse manualmente. El prefijo de la ruta del sistema de archivos es /var/lib/nethserver/vmail/.

Groups mailboxes

The automatic aliases for groups mailboxes are initially disabled. If enabled, addresses like <groupname>@<domain> become valid email addresses. A specific group address can be disabled and enabled again in a later stage, once Groups mailboxes are enabled. To disable the automatic aliases globally, refer to General settings.

A group mailbox has no disk space for it. When a message is sent to a group mailbox, a copy of it is delivered to the group members, according to their delivery and forward preferences.

Advertencia

If the system is bound to an Active Directory account provider the group mailbox works only if the group type is Security group. If the group type is Distribution group it does not work.

Public mailboxes

Nota

In the old Server Manager the Shared mailboxes label was used in place of Public mailboxes.

Public mailboxes can be shared among groups of users. The Email > Mailboxes > Public mailboxes section allows creating a new public mailbox and defining one or more owning groups. Public mailboxes can also be created by any IMAP client supporting IMAP ACL protocol extension (RFC 4314).

General settings

The Email > Mailboxes [General settings] > Configure page controls what protocols are available to access the user’s mailbox:

  • IMAP 12 (recomendado)

  • POP3 13 (obsoleto)

For security reasons, all protocols require STARTTLS encryption by default. The Allow unencrypted connections check box, disables this important requirement, and allows passing clear-text passwords and mail contents over the network.

Advertencia

¡No permita conexiones no cifradas en entornos de producción!

From the same page, the Quota limit for each mailbox can be limited to a default quota. If the general mailbox quota is enabled, the Email > Mailboxes list summarizes the quota usage for each user. This summary is updated when a user logs in or a message is delivered. The quota can be customized for a specific user in Email > Mailboxes [users item] > Edit > Custom mailbox quota.

Messages marked as spam (see Filtro) can be automatically moved into the Junk folder by enabling the option Move spam to «Junk» folder. Spam messages are expunged automatically after the Keep spam for period has elapsed. The spam retention period can be customized for a specific user in Email > Mailboxes [users item] > Edit > Custom spam retention.

The root user can impersonate another user, gaining full rights to any mailbox contents and folder permissions. The Root can log in as another user option controls this empowerment, known also as master user in Dovecot 2.

Cuando Root puede iniciar sesión como otro usuario está habilitado, las siguientes credenciales son aceptadas por el servidor IMAP:

  • Nombre de usuario con el sufijo `` *root`` añadido

  • Contraseña de root

Por ejemplo, para acceder como john con la contraseña root secr3t, utilice las siguientes credenciales:

  • Nombre de usuario: john*root

  • Contraseña: secr3t

Additional options:

  • If Groups mailboxes were enabled in Email > Mailboxes > Groups, unselect the Automatic alias for groups check box to disable them again.

  • It is possible to record the IMAP actions by enabling Log IMAP actions. See also Logs.

  • A diferencia de casi cualquier cliente IMAP, Outlook no mueve los mensajes eliminados a la papelera, pero simplemente los marca como «eliminados».

    It is possibile to automatically move messages inside the trash folder, by enabling Move deleted email to trash (Outlook).

    You should also change Outlook configuration to hide deleted messages from the inbox folder. This configuration is available in the Outlook options menu.

  • Max user connections per IP changes the limit of connections for a user coming from the same IP address. This limit could be increased if messages like Maximum number of connections appear in the log files (see Logs).

Shared seen configuration

Users could share their mailbox (or some parts of it, folders) with selected accounts on the system. Everyone who is given access to a shared mailbox can read or delete messages according to permissions granted by the mailbox owner.

An IMAP flag named /Seen is used to mark if a message has been read or not. In a shared mailbox, each user has their copy of the messages they have read, but sometimes a team sharing a mailbox could prefer to know if a mail has already been read by someone else. To enable sharing of the /Seen flag for all shared mailboxes use the following commands:

config setprop dovecot SharedSeen enabled
signal-event nethserver-mail-server-save

Please note that changing the SharedSeen status resets the /Seen flag for all users on all mailboxes.

Public folders are created by the administrator and are usually visible to all users (or large groups). The /Seen flag is kept for each user and it cannot be shared.

Addresses

In addition to the Users, Groups and Public mailboxes addresses, described in the previous section, the system enables the creation of an unlimited number of email addresses, from the Email > Addresses page. Each mail address is associated with one or more destinations. A destination can be of the following types:

  • user mailbox

  • groups mailbox

  • public mailbox

  • external email address

A mail address can be bound to any mail domain or be specific to one mail domain. For example:

  • First domain: mydomain.net

  • Second domain: example.com

  • Email address info bound to any domain: info@mydomain.net, info@example.com

  • Email address goofy specific to one domain: goofy@example.com

Sometimes a company forbids communications from outside the organization using personal email addresses. The Internal check box (formerly Local network only) and the Make internal and Make public action buttons block the possibility of an address to receive messages from the outside. Still an internal address can be used to exchange messages with other accounts of the system.

Connectors

The POP3/IMAP connector is accessible under the Email > Connectors page.

Configured external accounts will be checked regularly and retrieved messages will be delivered to local users.

It is not recommended to use the POP3 connector as the primary method for managing email. Mail delivery can be affected by disk space and connectivity problems of the provider’s server. Also, the spam filter will be less effective due to the original email envelope information becoming lost.

POP3/IMAP accounts are configured from POP3 connector > Accounts page. Each account can be specified:

  • the email address (as unique account identifier)

  • the protocol (IMAP/POP3/IMAP with SSL/POP3 with SSL)

  • the remote server address

  • the account credentials

  • the local user account where to deliver messages

  • if a message has to be deleted from the remote server after delivery

  • antispam and antivirus checks

Nota

It is allowed to associate more than one external accounts to a local one. Deleting an account will not delete already delivered messages.

After the account configuration has been completed, the account is automatically checked for new mail.

The underneath implementation is based on Getmail. After fetching mail messages from the POP3/IMAP provider Getmail applies all required filters (SPAM and virus) prior to delivering the mail locally. All messages are filtered according to the configured rules.

All operations are logged in /var/log/maillog.

Advertencia

If an account was selected for delivery and has been subsequently deleted the configuration becomes inconsistent. If this should happen then existing account configuration in POP3 connector page must be disabled or deleted.

Synchronization

The Email > Synchronization page is based on an IMAP transfer tool called Imapsync. The purpose is to migrate email messages from a remote IMAP account to a local one.

The migration is recursive and incremental and can be repeated as many times as needed. The emails will be copied locally if they do not exist on the local server.

The system administrator of the local NethServer does not need to know the password of the local user. However, the administrator has to know the password of the remote IMAP account, unless the IMAP admin authentication is implemented also for the remote email server.

If the remote IMAP server is also a NethServer, the IMAP admin user is vmail and its password can be read from /var/lib/nethserver/secrets/vmail. The username with a *vmail suffix (e.g. username@domain.com*vmail) and the vmail password has to be set in the IMAP synchronization panel.

Nota

List of IMAP servers with admin authentication in Imapsync documentation

Queue

The Email > Queue page lists the messages that are waiting to be relayed in the SMTP mail queue. In normal conditions, this queue should be empty or contain just a few messages.

The Email > Queue [Charts] > Show charts link shows a real-time chart of the mail queue status in the last minutes, updated as the page is left opened. The chart shows the number of message in the queue and the total queue size in kilobytes.

While messages are in the queue, the administrator can request an immediate message relay attempt, by pressing the button Resend all (formerly Attempt to send), or empty the queue with the Delete all button.

It is also possible to selectively Resend or Delete a queued message, from the action buttons of Email > Queue [List] items.

Relay

The Email > Relay page configures how messages are accepted and routed from the NethServer SMTP server to other SMTP servers.

Políticas especiales de acceso SMTP

The default NethServer configuration requires that all clients use the submission port (587) with encryption and authentication enabled to send mail through the SMTP server. See also Configuración del cliente.

To ease the configuration of legacy environments, the Email > Relay [Configuration] > Details section (formerly the Email > SMTP access page) allows making some exceptions on the default SMTP access policy.

Advertencia

¡No cambie la política predeterminada en nuevos entornos!

For instance, there are some devices (printers, scanners, …) that do not support SMTP authentication, encryption or port settings. Those can be enabled to send email messages by listing their IP address in Allow relay from IP addresses text area.

Advertencia

The listed IP addresses are excluded from all mail filtering checks: use this feature only as a last resort

Moreover, in the same section there are further options:

  • La opción Permitir la retransmisión desde redes de confianza permite a cualquier cliente de las redes de confianza enviar mensajes de correo electrónico sin ninguna restricción.

  • La opción Habilitar la autenticación en el puerto 25 permite a los clientes SMTP autenticados enviar mensajes de correo electrónico también en el puerto 25.

  • By default an authenticated SMTP client has no particular restrictions on setting the SMTP sender address.

    To avoid the unauthorized use of email addresses and the sender address spoofing, enable the Enforce sender/login match option.

    If enabled, only addresses associated to the current SMTP login are allowed.

HELO personalizada

The first step of an SMTP session is the exchange of HELO command (or EHLO). This command takes a valid server name as required parameter (RFC 1123).

NethServer y otros servidores de correo intentan reducir el spam al no aceptar dominios HELO que no estén registrados en un DNS público.

When talking to another mail server, NethServer uses its full host name (FQDN) as the value for the HELO command. If the FQDN is not registered in the public DNS, the HELO can be changed in the Custom HELO text field.

Esta configuración también es valiosa si el servidor de correo está utilizando un servicio DNS dinámico gratuito.

Relay hosts

The Email > Relay page allows to describe the route of an email message, by sending it through an external relay host with specific port, authentication, and TLS settings.

Create a relay host description under Email > Relay > Create relay host.

The relay host is identified by the SMTP sender address. It is possible to match the full sender address or only the domain part of it.

Default relay host settings

If the sender address does not match the relay rules described in the above section it is possible (though not recommended) to configure a default relay host instead of relying on the standard SMTP relay rules.

Nota

Por lo general, no se recomiendan envíos a través de smarthost. Puede ser utilizado sólo si el servidor está temporalmente en la lista negra 14, o el acceso SMTP normal está restringido por el ISP.

The System > Settings > Smart host section, configures the outgoing messages to be directed through a special SMTP server, technically named smarthost. A smarthost accepts to relay messages under some restrictions. It could check:

  • the client IP address

  • the client SMTP AUTH credentials

Refer also to Smart host for more information.

Settings

From the Email > Settings page, the Maximum message size (formerly Queue message max size) slider sets the maximum size of messages traversing the system. If this limit is exceeded, a message cannot enter the system at all and is rejected.

Una vez que un mensaje entra en NethServer, se mantiene en una cola, esperando la entrega final o la retransmisión. Cuando NethServer retransmite un mensaje a un servidor remoto, pueden producirse errores. Por ejemplo,

  • La conexión de red falla, o

  • the other server is down or is overloaded

Those and other errors are temporary: in such cases, NethServer attempts to reconnect the remote host at regular intervals until a limit is reached. The Message queue lifetime (formerly Queue message lifetime) slider changes this limit. By default it is set to 4 days.

To keep an hidden copy of any message traversing the mail server, enable the Forward a copy of all messages (formerly Always send a copy (Bcc) check box). This feature is different from the same check box under Email > Domains as it does not differentiate between mail domains and catches also any outgoing message.

Advertencia

On some countries, enabling the Forward a copy of all messages can be against privacy laws.

Logs

Cada operación del servidor de correo se guarda en los siguientes archivos de registro:

  • /var/log/maillog registra todas las transacciones de correo

  • /var/log/imap contains users login and logout operations, plus the IMAP actions, if enabled in General settings

A transaction recorded in the maillog file usually involves different components of the mail server. Each line contains respectively

  • the timestamp

  • the host name

  • El nombre del componente y el ID de proceso de la instancia de componente

  • Un mensaje de texto que detalla la operación

NethServer configuration uses Rspamd as milter. It runs an Rspamd proxy worker in «self-scan» mode 19.

The key to track the whole SMTP transaction, including Rspamd decisions is the message ID header, or the Postfix Queue ID (QID). Both are available from the message source. The Message-ID header is generated by the sender, whilst the QID is assigned by the receiving MTA. For instance

Received: from my.example.com (my.example.com [10.154.200.17])
      by mail.mynethserver.org (Postfix) with ESMTP id A785B308622AB
      for <jsmith@example.com>; Tue, 15 May 2018 02:05:02 +0200 (CEST)
...
Message-ID: <5afa242e.hP5p/mry+fTNNjms%no-reply@example.com>
User-Agent: Heirloom mailx 12.5 7/5/10

Here A785B308622AB is the QID, whilst 5afa242e.hP5p/mry+fTNNjms%no-reply@example.com is the Message ID.

Both strings can be used with the grep command to find relevant log lines in /var/log/maillog* (note the ending «*» to search also in archived log files). For instance

grep -F 'A785B308622AB' /var/log/maillog*

Yields

/var/log/maillog:May 15 02:05:02 mail postfix/smtpd[25846]: A785B308622AB: client=my.example.com[10.154.200.17]
/var/log/maillog:May 15 02:05:02 mail postfix/cleanup[25849]: A785B308622AB: message-id=<5afa242e.hP5p/mry+fTNNjms%no-reply@example.com>
/var/log/maillog:May 15 02:05:02 mail rspamd[27538]: <8ae27d>; proxy; rspamd_message_parse: loaded message; id: <5afa242e.hP5p/mry+fTNNjms%no-reply@example.com>; queue-id: <A785B308622AB>; size: 2348; checksum: <b1035f4fb07162ba88053d9e38df9c93>
/var/log/maillog:May 15 02:05:03 mail rspamd[27538]: <8ae27d>; proxy; rspamd_task_write_log: id: <5afa242e.hP5p/mry+fTNNjms%no-reply@example.com>, qid: <A785B308622AB>, ip: 10.154.200.17, from: <no-reply@example.com>, (default: F (no action): [-0.64/20.00] [BAYES_HAM(-3.00){100.00%;},AUTH_NA(1.00){},MID_CONTAINS_FROM(1.00){},MX_INVALID(0.50){},MIME_GOOD(-0.10){text/plain;},IP_SCORE(-0.04){ip: (0.22), ipnet: 10.154.192.0/20(0.18), asn: 14061(0.23), country: US(-0.81);},ASN(0.00){asn:14061, ipnet:10.154.192.0/20, country:US;},DMARC_NA(0.00){example.com;},FROM_EQ_ENVFROM(0.00){},FROM_NO_DN(0.00){},NEURAL_HAM(-0.00){-0.656;0;},RCPT_COUNT_ONE(0.00){1;},RCVD_COUNT_TWO(0.00){2;},RCVD_NO_TLS_LAST(0.00){},R_DKIM_NA(0.00){},R_SPF_NA(0.00){},TO_DN_NONE(0.00){},TO_DOM_EQ_FROM_DOM(0.00){},TO_MATCH_ENVRCPT_ALL(0.00){}]), len: 2348, time: 750.636ms real, 5.680ms virtual, dns req: 47, digest: <b1035f4fb07162ba88053d9e38df9c93>, rcpts: <jsmith@example.com>, mime_rcpts: <jsmith@example.com>
/var/log/maillog:May 15 02:05:03 mail postfix/qmgr[27757]: A785B308622AB: from=<no-reply@example.com>, size=2597, nrcpt=1 (queue active)
/var/log/maillog:May 15 02:05:03 mail postfix/lmtp[25854]: A785B308622AB: to=<vmail+jsmith@mail.mynethserver.org>, orig_to=<jsmith@example.com>, relay=mail.mynethserver.org[/var/run/dovecot/lmtp], delay=0.82, delays=0.8/0.01/0.01/0.01, dsn=2.0.0, status=sent (250 2.0.0 <vmail+jsmith@mail.mynethserver.org> gK8pHS8k+lr/ZAAAJc5BcA Saved)
/var/log/maillog:May 15 02:05:03 mail postfix/qmgr[27757]: A785B308622AB: removed

Configuración del cliente

El servidor admite clientes de correo electrónico estándar que cumplan con los siguientes puertos IANA:

  • imap/143

  • pop3/110

  • smtp/587

  • sieve/4190

La autenticación requiere el comando STARTTLS y admite las siguientes variantes:

  • LOGIN

  • PLAIN

  • GSSAPI (only if NethServer is bound to Samba/Microsoft Active Directory)

También los siguientes puertos habilitados para SSL están disponibles para software heredado que aún no admite STARTTLS:

  • imaps/993

  • pop3s/995

  • smtps/465

Advertencia

The standard SMTP port 25 is reserved for mail transfers between MTA servers. Mail user agents (MUA) must use the submission port.

Kerberos-based authentication

Mail services can authenticate users of Active Directory with the Kerberos single-sign-on protocol.

Both local and remote Active Directory accounts provider need an additional and manual step to complete the GSSAPI/Kerberos setup of IMAP, POP and SMTP services.

  1. In NethServer shell authenticate as an AD domain administrator

    kinit some_domain_admin

  2. Add the service principals for the mail services to the machine account

    net ads setspn add $(hostname -s) imap/$(hostname -f)
net ads setspn add $(hostname -s) pop/$(hostname -f)
net ads setspn add $(hostname -s) smtp/$(hostname -f)

  3. Terminate the session

    kdestroy

Referencias

1

Postfix mail server http://www.postfix.org/

2(1,2)

Dovecot Secure IMAP server http://www.dovecot.org/

3

Lenguaje de filtrado de correo https://en.wikipedia.org/wiki/Sieve_(mail_filtering_language)

4(1,2,3)

Rspamd – Fast, free and open-source spam filtering system. https://rspamd.com/

5

Correo electrónico, https://es.wikipedia.org/wiki/Correo_electrónico

6

El registro MX DNS, https://es.wikipedia.org/wiki/MX_(registro)

7

SMTP, https://es.wikipedia.org/wiki/Simple_Mail_Transfer_Protocol

8(1,2)

Domain Keys Identified Mail (DKIM) is an email authentication method designed to detect email spoofing – Wikipedia

9

El formato Maildir, https://es.wikipedia.org/wiki/Maildir

10

alterMIME is a small program which is used to alter your mime-encoded mailpack – https://pldaniels.com/altermime/

11

La sintaxis de formato de texto plano Markdown, https://es.wikipedia.org/wiki/Markdown

12

IMAP https://es.wikipedia.org/wiki/Internet_Message_Access_Protocol

13

POP3 https://es.wikipedia.org/wiki/Post_Office_Protocol

14(1,2)

DNSBL https://en.wikipedia.org/wiki/DNSBL

15

SPAM https://es.wikipedia.org/wiki/Spam

16

Greylisting is a method of defending e-mail users against spam. A mail transfer agent (MTA) using greylisting will «temporarily reject» any email from a sender it does not recognize – Wikipedia

17

Filtrado Bayesiano https://en.wikipedia.org/wiki/Naive_Bayes_spam_filtering

18

Las formas maravillosas de un correo electrónico https://workaround.org/ispmail/wheezybig-picture/

19

https://rspamd.com/doc/workers/rspamd_proxy.html