nethserver-mail

Mail system implementation based on Postfix, Dovecot, Rspamd, OpenDKIM. The mail system configuration is splitted into many RPMs, described in the following sections.

• nethserver-mail-common
• nethserver-mail-smarthost
• nethserver-mail-disclaimer
• nethserver-mail-filter
• nethserver-mail-server
• nethserver-mail-ipaccess
• nethserver-mail-getmail
• nethserver-mail-p3scan
• mail-quarantine
• Database format
  • configuration
  • domains
  • accounts
  • getmail
  • quarantine
• Mail quota
• Disabled users
• Testing Dovecot with Mutt
• Set special ACL on mailboxes
• IP-based IMAP access restriction
  • Syntax of /etc/dovecot/ipaccess.conf
• Enable dovecot IMAP rawlog
• Access the rspamd UI
• Bayesian rules upgrade to rspamd
• Sender address validation
• Postfix SMTP listening ports
• Dynamic group aliases

nethserver-mail-common

• Common infrastructure for nethserver-mail-server and nethserver-mail-filter, Postfix-based.
• Relay
• Queue parameters: age + message size
• MX record configuration

nethserver-mail-smarthost

• Send mail through the given MTA (smarthost), with SMTP/AUTH
• StartTLS encryption
• Set sender address for mail sent from root user (see Notifications section under nethserver-base package README)

nethserver-mail-disclaimer

• Attach disclaimer/legal notice to outbound messages for certain domains
• Runs altermime with Postfix content_filter option

nethserver-mail-filter

• Based on Rspamd
• Anti-spam with DNSBL (see: nethserver-unbound)
• Anti-virus
• Attachment block
• Real-time Blackhole List (RBL) (default disabled)
• Sender Policy Framework (SPF) (default disabled)
• Customized spam threshold
• Sender WBL, Recipient whitelist

nethserver-mail-server

• IMAP/POP3 mailbox access protocols
• STARTTLS enabled by default
• Mail quota
• Sieve filters
• Postfix/dovecot-lda integration
• Multi-domain
• Domain-specific configuration
• Pseudonyms
• SMTP authentication
• Active Directory integration
• SpamAssassin's Bayesian classifier training (spamtrainers group)
• Spam retention time
• Sender address restriction based on login name
• Dynamic group members address list expansion

nethserver-mail-ipaccess

IMAP access for a specific group of users. See IP-based IMAP access restriction.

nethserver-mail-getmail

The package configures getmail using cron.

For each enabled account the system:

• generates a .cfg file inside the /var/lib/getmail directory from the template /etc/e-smith/templates/getmailrc
• adds a line inside the /etc/cron.d/getmail, all getmail instances use a non-blocking flock
• delivers the messages using dovecot-lda

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

If a virus is found inside a received mail, the message is dropped.

The evidence of log in /var/log/maillog:

Feb 14 18:19:10 vm5 clamd[1791]: instream(local): Eicar-Test-Signature FOUND

nethserver-mail-p3scan

This package configures p3scan, full-transparent POP3 proxy-server for email clients.

• POP3 and POP3s proxy
• Anti-virus and anti-spam checks

mail-quarantine

This package makes a quarantine for spam. They are sent to a mailbox (you need to manually created it), waiting a review of the sysadmin. If enabled a mail notification is sent to the postmaster (root alias) for each quarantined email.

Database format

configuration

Postfix example:

postfix=service
   ...
   AccessPolicies=
   AlwaysBccStatus=disabled
   AlwaysBccAddress=
   MessageQueueLifetime=4
   MessageSizeMax=20000000
   ConnectionsLimit=
   ConnectionsLimitPerIp=
   SystemUserRecipientStatus=disabled
   ...
   SenderValidation=disabled
   DynamicGroupAlias=disabled
   HeloHost=
   SmartHostAuth=disabled
   SmartHostAuthStatus=disabled
   SmartHostName=192.168.5.252
   SmartHostPassword=password
   SmartHostPort=25
   SmartHostStatus=disabled
   SmartHostTlsStatus=enabled
   SmartHostUsername=ns1

• AccessPolicies: A comma separated list of values. Obsoletes SubmissionPolicyType prop. Currently defined values are smtpauth and trustednetworks.
• smtpauth enable SMTP/AUTH on port 25, otherwise it is enabled only on 587 and 465 submission ports
• trustednetworks allow relay from any host in trusted networks (green network included).
• AlwaysBccStatus {enabled,disabled}: if enabled any message entering Postifx mail system is copied to the given AlwaysBccAddress.
• AlwaysBccAddress: an email address that always receives a message copy (controlled by AlwaysBccStatus).
• SystemUserRecipientStatus {enabled,disabled} enabled, accept from any network the recipient addresses formed by user account names and domain part localhost, localhost.<domainname> and FQDN hostname.
• SenderValidation {enabled,disabled}, default disabled, checks the SMTP sender is consistent with /etc/login_maps and /etc/login_maps.pcre contents.

• DynamicGroupAlias {enabled,disabled}, default disabled,

  if enabled, create distribution lists based on system groups. See also the "Dynamic group aliases" section below.

• HeloHost. FQDN hostname used by Postfix when connecting to other MTAs

Dovecot example:

dovecot=service
    ...
    AdminIsMaster=disabled
    DeletedToTrash=disabled
    FtsLuceneStatus=enabled
    ImapStatus=enabled
    LmtpInetListenerStatus=disabled
    LogActions=disabled
    MaxProcesses=400
    MaxUserConnectionsPerIp=12
    PopStatus=enabled
    QuotaDefaultSize=20
    QuotaStatus=disabled
    SharedMailboxesStatus=enabled
    SpamFolder=Junk
    SpamRetentionTime=15d
    TlsSecurity=required
    RestrictedAccessGroup=

Properties:

• AdminIsMaster {enabled,disabled} allow root user to impersonate other users
• DeletedToTrash {enabled,disabled} deletedtotrash plugin
• FtsLuceneStatus {enabled,disabled} lucene indexed search plugin
• ImapStatus {enabled,disabled} IMAP protocol switch
• LmtpInetListenerStatus {enabled,disabled} open a TCP socket for LMTP protocol
• LogActions {enabled,disabled} IMAP actions logging plugin
• MaxProcesses N maximum number of worker processes spawned by dovecot. A single user session usually requires multiple processes.
• MaxUserConnectionsPerIp N maximum TCP connections for one user behind the same IP
• PopStatus {enabled,disabled} POP3 protocol switch
• QuotaDefaultSize N Default user quota size (1 unit is 10MB)
• QuotaStatus {enabled,disabled} General user mail quota switch
• SharedMailboxesStatus {disabled,enabled} Control the "Shared" IMAP namespace for per-user folder sharing
• SpamFolder FolderName Deliver spam tagged messages to the given folder (applied to all users)
• SpamRetentionTime Nd Expunge messages in SpamFolder if older than the given time span. "d" is for days.
• TlsSecurity {optional,required} controls dovecot disable_plaintext_auth parameter: if set to required clear-text authentication methods are disabled, while optional enables them.
• RestrictedAccessGroup The value is a long group name, like domain [email protected]. Members of the given group can login to dovecot services only from trusted networks. Install the nethserver-mail-server-ipaccess package to enable this feature.

p3scan example:

p3scan=service
  SSLScan=enabled
  SpamScan=enabled
  TCPPort=8110
  Template=/etc/p3scan/p3scan-en.mail
  VirusScan=enabled
  access=
  status=enabled

rspamd example:

rspamd=service
    BlockAttachmentClassList=Exec
    BlockAttachmentCustomList=doc,odt
    BlockAttachmentCustomStatus=disabled
    BlockAttachmentStatus=enabled
    OletoolsStatus=enabled
    Password=uO9QjlnRCDsT0ZCD
    RecipientWhiteList=
    SenderBlackList=
    SenderWhiteList=
    SpamCheckStatus=enabled
    SpamDsnLevel=20
    SpamGreyLevel=4
    SpamKillLevel=15
    SpamSubjectPrefixStatus=disabled
    SpamSubjectPrefixString=***SPAM***
    SpamTag2Level=6
    SpamTagLevel=2
    VirusAction=reject
    VirusCheckStatus=enabled
    VirusScanOnlyAttachment=false
    VirusScanSize=20000000
    status=enabled

Properties:

• BlockAttachmentClassList {Exec,Arch} Reject the attachements matching the extension list
• BlockAttachmentCustomList List Reject the attachements matching the custom extension list
• BlockAttachmentCustomStatus {enabled,disabled} Enable the custom list of rejected extensions
• OletoolsStatus {enabled,disabled} Enable Oletools to reject suspicious microsoft office document macro
• Password Password to authenticate the user rspamd for the Rspamd UI
• RecipientWhiteList Do not perform checks for the recipient list, always accept
• SenderBlackList Do not perform checks for the sender list, always reject
• SenderWhiteList Do not perform checks for the sender list, always accept
• SpamCheckStatus {enabled,disabled} Enable the SPAM filter
• SpamSubjectPrefixStatus {enabled,disabled} Enable to rewrite the subject when a possible spam is detected
• SpamSubjectPrefixString string Rewrite the subject with the string when a possible spam is detected
• VirusAction Possible action when a virus is detected (reject is default, 'rewrite_subject' to tag as spam)
• VirusCheckStatus {enabled,disabled} Enable the virus check with Clamav
• VirusScanOnlyAttachment {true,false} If true only messages with non-image attachments will be checked
• VirusScanSize The messages > n bytes in size are not scanned (valuable for Clamav and Oletools)

domains

Record of type domain:

internal.tld=domain
  ...
  TransportType=none

mycompany.com=domain
  ...
  TransportType=Relay
  RelayHost=10.1.1.4
  RelayPort=25
  DisclaimerStatus=disabled

test.tld=domain
  ...
  TransportType=SmtpSink

example.com=domain
  ...
  TransportType=LocalDelivery
  UnknownRecipientsActionType=deliver
  UnknownRecipientsActionDeliverMailbox=jdoe
  AlwaysBccStatus=enabled
  AlwaysBccAddress=admin``there.org

other.net=domain
  ...
  TransportType=Relay
  RelayHost=mail.other.net
  RelayPort=25

accounts

Groups:

[email protected]=group
   ...
   MailStatus=enabled
   MailAccess=private

[email protected]=group
   ...
   MailStatus=enabled
   MailAccess=public

[email protected]=group
   ...
   MailStatus=enabled
   MailAccess=public

User:

jdoe=user
   FirstName=John
   LastName=Doe
   ...
   MailStatus=enabled
   MailQuotaType=custom
   MailQuotaCustom=15
   MailForwardStatus=disabled
   MailForwardAddress=
   MailForwardKeepMessageCopy=no

and his pseudonyms: ::

 john.doe``example.com=pseudonym
   Account=jdoe
   ControlledBy=system
   Access=public

 doe``=pseudonym
   Account=jdoe
   ControlledBy=operators
   Access=private

getmail

All records of type getmail are saved inside the getmail database.

Properties:

• The key is the mail account to be downloaded
• status: can be enabled or disabled, default is enabled
• Account: local user where messages will be delivered. Should be in the form user@domain
• Server: server of the mail account
• Username: user name of the mail account
• Password: password of the mail account
• Delete: numbers of days after downloaded messages will be deleted, -1 means never, 0 means immediately
• Time: integer number rappresenting the minutes between each check, valid valued are between 1 and 60
• FilterCheck: if enabled, check downloaded messages for viruses and spam using rspamc classifier

• Retriever: can be any getmail retriever, see Getmail official doc

  Retrievers available in the web interface:

  • SimplePOP3Retriever
  • SimplePOP3SSLRetriever
  • SimpleIMAPRetriever
  • SimpleIMAPSSLRetriever

Example:

db getmail set [email protected] getmail Account [email protected] status enabled Password Nethesis,1234 Server localhost Username [email protected] Retriever SimplePOP3Retriever Delete enabled Time 30 VirusCheck enabled SpamCheck enabled

quarantine

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

   rspamd=service
   ...
   QuarantineAccount=vmail+quarantine
   QuarantineSelector=is_reject
   QuarantineStatus=enabled
   SpamNotificationStatus=disabled


* ``QuarantineAccount``: The local email box where to send all spams (spam check is automatically disabled on this account). You must create it manually. You could send it to an external mailbox  but then you must disable the spam check on this server
* ``QuarantineSelector``: It is possible to move to quarantine all spams (add_header, rewrite_subject, reject), allowed values are ``is_reject`` (default) or ``is_spam``
* ``QuarantineStatus``: Enable the quarantine, spam are no more rejected: enabled/disabled (default)
* ``SpamNotificationStatus``: Enable the email notification when email are quarantined: enabled/disabled (default)

For example, the following commands enable the quarantine: ::

config setprop rspamd QuarantineAccount [email protected] QuarantineStatus enabled SpamNotificationStatus enabled signal-event nethserver-mail-quarantine-save

Mail quota

The default mail quota is configured in dovecot.conf. Custom user mail quota is set by the dovecot-postlogin script, by reading /etc/dovecot/user-quota (which is a template). If a custom mail quota is set the UI interface does not show the updated value until the user performs an IMAP login.

Disabled users

By default all system users are also Dovecot users. To disable a user we configure a blacklist in dovecot.conf: /etc/dovecot/deny.passwd.

As Dovecot is configured as authentication backend for Postfix, a disabled user loses also SMTP AUTH access.

Testing Dovecot with Mutt

Read admin's mail with Mutt IMAP client. Quickstart:

yum install mutt
cat - <<EOF > ~/.muttrc
set spoolfile="imaps://root@localhost/"
set folder=""
EOF
mutt

See: http://dev.mutt.org/doc/manual.html

When mutt starts always asks for the root password. To avoid typing the password again and again write it in .muttrc:

set spoolfile="imaps://root:PASSWORD@localhost/"
set folder=""

PASSWORD must be URL-encoded. For instance the slash character / is encoded as %2f.

Set special ACL on mailboxes

The nethserver-mail-shrmbx-modify action applies some predefined ACL settings to shared mailboxes (type the mailbox name twice: the action performs also rename):

/etc/e-smith/events/actions/nethserver-mail-shrmbx-modify EVENT OLDNAME NEWNAME ID PERM [ID PERM ...]

For instance, let's grant full "admin" permissions to group "administrators":

/etc/e-smith/events/actions/nethserver-mail-shrmbx-modify ev 'Public folder1' 'Public Folder One' group=administrators@$(hostname -d) ADMIN

You can also use doveadm to set special ACL on a shared mailbox:

doveadm acl set -u <user> <shared_mailbox> <subject> <flags>

Example: allow insert and expunge to user goofy on public mailbox testshare (domain of the machine is local.nethserver.org):

doveadm acl set -u [email protected] Public/testshare "[email protected]" insert expunge

IP-based IMAP access restriction

This feature allows to restrict IMAP access for a specific group. Members of the given group have IMAP access restricted to trusted networks.

1. Install nethserver-mail-ipaccess package

   yum install nethserver-mail-ipaccess
   

2. Set the limited group, remember to use the full group name: <group>@<domain>

   config setprop dovecot RestrictedAccessGroup <group>@<domain>
   

   Example for group [email protected]:

   config setprop dovecot RestrictedAccessGroup [email protected]
   

3. Apply the configuration

   signal-event nethserver-mail-server-save
   

Syntax of /etc/dovecot/ipaccess.conf

The dovecot-postlogin script enforces an IP-based access policy to dovecot services when the file :file:/etc/dovecot/ipaccess.conf exists and is readable.

The file is composed by comments and records. Comments are line starting with #, whilst records have the following syntax:

<long group name> = <cidr list>

A long group name is the group name with domain suffix, like domain [email protected].

The cidr list is a comma-separated list of IP and network addresses in CIDR format, like 127.0.0.1, 192.168.1.0/24, 10.1.1.2. The binary conversion is implemented by the NetAddr::IP Perl module. See perldoc NetAddr::IP for details.

Enable dovecot IMAP rawlog

This section describes how to record the list of IMAP commands sent by the client and the server during an IMAP session. For more information see Dovecot rawlog.

Create the file /etc/e-smith/templates-custom/etc/dovecot/dovecot.conf/90rawlog with the following contents:

#
# 90rawlog (custom)
#
import_environment = $import_environment DEBUG=1

service imap-postlogin \{
  executable = script-login -d rawlog -t /usr/libexec/nethserver/dovecot-postlogin
\}

Apply the new configuration

signal-event nethserver-mail-server-save

To enable IMAP rawlog for a specific user, identify the user (vmail) home directory with the following command:

# doveadm user -u [email protected]
userdb: [email protected]
system_groups_user: [email protected]
uid       : 987
gid       : 990
home      : /var/lib/nethserver/vmail/[email protected]

Warning

Always use the user long name form, which includes the @domain suffix. In our example first.user would not work

Create the dovecot.rawlog directory and change permissions:

mkdir "/var/lib/nethserver/vmail/[email protected]/dovecot.rawlog"
chown vmail:vmail "/var/lib/nethserver/vmail/[email protected]/dovecot.rawlog"

Detailed IMAP rawlogs are now created under the user's (vmail) home directory. Each session is split into two files: .in file for client requests, .out file for server responses. For instance,

/var/lib/nethserver/vmail/[email protected]/dovecot.rawlog/20180913-143301-6293.in
/var/lib/nethserver/vmail/[email protected]/dovecot.rawlog/20180913-143301-6293.out

The initial timestamp helps to mix them together and obtain the complete IMAP session trace:

sort -n /var/lib/nethserver/vmail/[email protected]/dovecot.rawlog/20180913-143301-6293.*

Access the rspamd UI

The rspamd UI is available from the same httpd instance of Server Manager:

https://<IP>:980/rspamd

Access is granted to any account defined in /etc/httpd/admin-conf/rspamd.secret. By default a rspamd login is created automatically. Its password is available with the following command:

config getprop rspamd Password

Additional accounts can be created with the following command:

/usr/bin/htpasswd -b -m /etc/httpd/admin-conf/rspamd.secret username S3cr3t

If an account provider is configured, the default access policy to rspamd UI is granting access also to admin user and members of the domain admins group. Type config show admins for details.

Bayesian rules upgrade to rspamd

Each Junk (or junkmail) folder from users' accounts, if present, can be used to train the Rspamd Bayesian filter database, by running the attached script:

bash /usr/share/doc/nethserver-mail-server-*/bayes_training.sh

Sender address validation

If the postfix/SenderValidation prop is set to enabled the SMTP server restricts the Mail from command usage. The sender address must be associated with the SMTP login name. The login/sender match is specified in the following Postfix tables, both implemented with an e-smith template:

• /etc/postfix/login_maps
• /etc/postfix/login_maps.pcre

To enable the SenderValidation:

config setprop postfix SenderValidation enabled
signal-event nethserver-mail-server-update

Postfix SMTP listening ports

The Postfix SMTP server listens on the following TCP ports

• 25, standard SMTP port; used by other MTAs
• 587, standard SMTP submission port; STARTTLS required by default to protect login passwords; used by MUAs
• 465, standard SMTPS submission port; TLS always required at socket level; used by MUAs which not support STARTTLS
• 10587, additional SMTP submission port for localhost only; no TLS required; used by local mail applications

Dynamic group aliases

If the postfix/DynamicGroupAlias prop is enabled an additional virtual_alias_maps TCP table is available. It expands a long group name to the group members list with a getent group call. The table is implemented in :file:/usr/libexec/nethserver/postfix-get-group. Note that group members lists are returned by SSSD: as such they obey to its caching rules.

When the DynamicGroupAlias general switch is enabled, individual groups can be disabled and marked private. If MailStatus prop is disabled the group long name is not considered a valid email address anymore. The MailAccess prop works like the Access prop for user records: if set to private only authenticated SMTP clients are allowed to use it as recipient.

Accounts DB group props example:

[email protected]=group
   ...
   MailStatus=enabled
   MailAccess=private