Mailrelay

To include all senders of an e-mail domain in the allowlist, this entry is entered as Regular expression: »/.*@ttt-point\.de/ }}

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Configuration of the mailrelay

Last adaptation to the version: 14.0.0

New:

• Hinweis zur alternativen Aktivierung des Mailfilters

Last updated: 

12.7.1
• Where necessary, only certificates with a private key part are offered

notempty

This article refers to a Resellerpreview

12.7.1 12.5.1 12.2.3 12.2.2 11.8.8 11.8.4 11.8.2 11.8 11.7

Access: Admin Interface of the UTMUTM-IP:Port or UTM-URL:Port
Port as configured at Network / Appliance Settings / Webserver
Default-Port: 11115
i.e.: https://utm.ttt-point.de:11115
Default: https://192.168.175.1:11115 Applications Mailrelay

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Configuration of the Mailrelay

The Securepoint UTM appliance can receive emails using the mailrelay and forward them to a mail server in the internal network. The mail relay checks the received emails and divides them into an appropriate category. Based on the category, it is decided whether an email is forwarded to the internal mail server or not.
To protect against spam or to relieve the [Mailfilter] further options can be configured. More than 90% of spam does not come from regular mail servers, but rather from private and work computers compromised by viruses and Trojans. On the other hand, checking target email addresses, greylisting and the greeting pause have proven to be effective functions.

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Preconditions

Settings on the provider side

In order to ensure smooth participation in mail traffic, a number of requirements must be met:

• The UTM must have a fixed IP address. (e.g. 195.4.169.36)
• There is an A record on the DNS provider's server that resolves to this IP address. (Example query for the A-record:
  ‍

  
  >nslookup -q=a ttt-point.de
  Server: UnKnown
  Address: 192.168.175.1
  
  Not authorized answer:
  Name: ttt-point.de
  Address: 195.4.169.36
  ‍

  
  host -t a ttt-point.de
  ttt-point.de has address 195.4.169.36
  )
• There is an MX record on the DNS provider's server that resolves to this address. (Example query for the MX record:
  ‍

  
  >nslookup -q=mx ttt-point.de
  Server: UnKnown
  Address: 192.168.175.1
  
  Not authorized answer:
  ttt-point.de MX preference = 10, mail exchanger = mx01.ttt-point.de
  ‍

  
  host -t mx ttt-point.de
  ttt-point.de mail is handled by 10 mx01.ttt-point.de.
  )
• A PTR record exists on the Internet provider's server that resolves correctly to the DNS A record used in the MX record (reverse DNS). (Example query for the PTR record:
  ‍

  =
  >nslookup -q=ptr 195.4.169.36
  Server: UnKnown
  Address: 192.168.175.1
  
  Not authorized answer:
  36.169.4.195.in-addr.arpa name = mx01.ttt-point.de
  ‍

  
  host -t ptr 195.4.169.36
  36.169.4.195.in-addr.arpa domain name pointer mx01.ttt-point.de.
  )

These are all settings that have to be made by the provider and NOT on the Securepoint Appliance!

notempty

Note:

Since a certain amount of storage space must be available for rejected mails or mails that could not yet be delivered to the internal mail server, the hardware recommendations should be considered without fail!

➊ Email is sent
➋ DNS-MX record points to UTM
➌ Email is delivered to the UTM and processed (mail filter, greylisting, etc.)

➍

UTM delivers email to the internal mail server
(according to the path under Applications Mailrelay

SMTP routes

)

➎ Email query from the internal network
➏ Query is forwarded to the mail server that was specified as the SMTP route

➊ Email is sent
➋ DNS-MX record points to UTM
➌ Email is delivered to the UTM and processed (mail filter, greylisting, etc.)

➍

UTM delivers email to the external mail server
(according to the path under Applications Mailrelay

SMTP routes

)

➎ Email query from the internal network
➏ Query is forwarded to the mail server that was specified as the SMTP route

In both scenarios the DNS A record must point to the fixed IP address of the UTM

Set of rules

To allow access to the mail relay, the hosts authorized to send mail must be allowed access to the corresponding interface of the Securepoint appliance (depending on the zone in which the hosts are located) via the SMTP protocol. Depending on the requirements, this can be a single host (e.g. the mail server), a group of hosts or the entire network. It is important that all applications that are to send mails via the mail relay have entered the corresponding firewall interface as SMTP server or smarthost. For example, to allow the internal network access to the mail relay, the set of rules can be created with the predefined network groups:
Caption	Value	Description	Packetfilter UTMuser@firewall.name.fqdnFirewall Update rules # Source: Destination: Service: NAT Action Active: 1 internet external-interface smtp Accept On 2 internal-network internal-interface smtp Accept On
Active:	On	Activate rule so that the portfilter takes effect
Source:	Internet	Select Internet as the source
Destination:	external-interface	Select external-interface as the destination
Service:	smtp	Select smtp as the service
Action:	Accept	Mails that meet the corresponding conditions are accepted and forwarded
Logging:	None - Do not log	Logging is not required
Group:	default	The portfilter rule can be assigned to a group
The second rule that allows forwarding the emails to Outlook.
Active:	On	Activate rule so that the portfilter takes effect
Source:	internal-network	Select internal-network as the source
Destination:	internal-interface	Select internal-interface as the destination
Service:	smtp	Select smtp as the service
Action:	Accept	Mails that meet the corresponding conditions are accepted and forwarded
Logging:	None - Do not log	Logging is not required
Group:	default	The portfilter rule can be assigned to a group
notempty Note: If there is no other connection available besides the Internet connection with the IP over which the mail is sent, it must be ensured that ONLY the mail server is allowed to send mail via SMTP. Otherwise a single computer in the network compromised by a Trojan could seriously disrupt the sending of mails or even make it completely impossible, because it spreads spam and malware with the public IP and is listed on corresponding blocklists for spammers within a very short time.
notempty Important: There must be no port forwarding for SMTP. This would ensure that the mails are forwarded past the mail relay!

Email address

Under Network Appliance Settings Global email address: a postmaster address should be configured. Otherwise undeliverable mails will remain on the disk space. This can cause the available memory to become insufficient at some point and mails to no longer be accepted.

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Basic configuration of the mailrelay for receiving mails

The configuration of the mailrelay takes place under Applications Mailrelay .

General

General

Caption	Value	Description	Mailrelay UTMuser@firewall.name.fqdnApplications Mailrelay Log General settings of the mailrelay
Activate mail filter:	On	Akiviert den Mailfilter ‍ notempty New as of v14.0 Indentisch mit Applications Mailfilter  Area Einstellungen Abschnitt Allgemein Option Mailfilter für Mailrelay / Mail-Connector
SASL authentication:	Off	Enables SASL authentication, if activated
Postmaster Address:	admin-mail@anyideas.de	A correct email address must be stored here. This email address is specified in the Network Appliance Settings dialog in the Global email address field. Changes are only possible there.
Maximum message size:	20  Megabytes	Maximum size of the mails in megabytes accepted by the mail relay. A message appears in the mail filter view in the user interface about the rejection.
Preferred protocol for outbound email:	No preference	Specifies whether the mail relay should preferentially establish outgoing connections with a certain protocol. ‍ This setting should only changed from its default in special cases (e.g., IPv4 behind NAT) and if problems to deliver mail arise.
	IPv4	IPv4 is preferred as protocol (e.g. IPv4 behind NAT)
	IPv6	IPv6 is preferred as protocol
Outgoing Address:	/---	With multipath routing, an outgoing interface can be specified here by the IP address. Communication from the internal network then also runs via this IP address. Further settings must be made on the mail server and its firewall in order to accept mails from this IP address.
SPF/DKIM/DMARC checks:	Off	Enables filtering for corresponding DKIM/DMARC/SPF-results in Mailfilter rules when enabled. ‍ Adds RFC 8601 Authentication-Results Header to email. Not performed for mails sent by SASL-authenticated users or mails coming from "trusted hosts", i.e. hosts that have an entry in the relaying list with action RELAY and option "Connect" or no option. Further information in the article about Mailfilter

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Smarthost

Smarthost

Settings for a Smarthost are only required if such a setting is required for outgoing mails. This is the case, for example, if no own mail server is operated or no fixed public IP address is available.

Caption	Value	Description	Smarthost settings of the mailrelay
Enable Smarthost:	On	Activates the Smarthost function.
Smarthost:	smtp.anyideas.de	smtp.anyideas.de Mail server that is to receive and send outgoing mails.(sample address)
Port:	587	Mail port for external mail server 25: Default port for smtp (default) 465: default port for implicit TLS 587: default port for STARTTLS
Use implicit TLS	Off	By default (deactivated), a connection is first established via smtp and then attempts to initiate TLS encryption with the remote terminal.
	On	When activated, the connection is first encrypted with TLS before smtp communication is established. If the remote terminal does not control TLS, no connection is established. The TLS version is configured under Authentication Encryption .
Smarthost Verification:	None	There is no verification of the smarthost.
	pki	The smarthost is verified by default installed root CAs or a self-signed CA. CA: SystemCAs (Default) Alternatively, a CA (previously created or imported under Authentication Certificates ) can be selected for authentication.
	dane	Authenticates and uses TLS to DANE-compliant servers, if offered.
Enable Authentication:	On	Enables authentication on the smarthost mail server. TLS/SSL encryption is required for authentication
User:	Credentials	The user of the Smarthost
Password:	Credentials	The corresponding password
		Displays the password

Relaying

Relaying

Configuration Relaying

Relaying list

 Relaying list 

Here it is configured which mails are accepted by the Securepoint appliance and forwarded to the internal mail server. Relaying can be allowed for certain hosts or certain domains.
Add an entry with the button Add Domain / Host

Specification of the following values:

Caption	Value	Description	Add Domain / Host UTMuser@firewall.name.fqdnApplicationsMailrelay Add Domain / Host Dialog
Domain:	anyideas.de	Email domain name or IP address
Option:	NONE	The action is applied to all events.
	From	The sender domain is evaluated here. Example: Domain: ttt-point.de - This applies to all mails with the domain ttt-point.de in the sender. notempty Since the sender domain can easily be faked, this option is to be used only after careful examination.
	To	The recipient domain is evaluated here. Example: Domain: anyideas.de - This concerns all mails with the domain anyideas.de in the recipient.
	Connect	Here the IP, hostname or domain of the mail server that wants to deliver the mail is evaluated. Example: Domain: ttt-point.de - Affects all mails from mail servers in the domain ttt-point.de - regardless of the sender or recipient of the mail.
Action:	RELAY	Mails that meet the relevant conditions will be accepted and forwarded.
	REJECTED	Mails are rejected.
	OK	Mails are accepted and delivered to a local mailbox, but not forwarded.

In order to relay all mails intended for recipients of your own domain, the following entry must be configured:

Add Domain / Host
Domain:	anyideas.de
Option:	To
Action:	RELAY

Settings

Settings

Use exact domain name for relaying:
On The relay reacts only to the domain name entered in the list and not to unregistered subdomains or extensions.
Example: Domain entered in the relay list: anyideas.de

On accepted by mailrelay:	Off accepted by mailrelay:
@anyideas.de	@anyideas.de @support.anyideas.de @anyideas.de.com

TLS Settings

TLS Settings

Caption	Default	Description
TLS encryption as server:	On	If TLS is deactivated, mails are sent over unencrypted connections!
Certificate: ‍ Only certificates with a private key part can be selected	default	The mailrelay uses a self-signed certificate for transport encryption. Optionally, a certificate whose CN corresponds to the UTM host name can be imported under Authentication Certificates .
TLS authentication as client:	may	Uses TLS if it is offered.
	encrypt	Always uses TLS. Connection with servers that do not offer TLS will be cancelled.
	dane	Authenticates and uses TLS to DANE-compliant servers, if offered.

SMTP Routen

SMTP Routen

SMTP Routing List

 SMTP Routing List 

Mailrelay UTMuser@firewall.name.fqdnApplications Mailrelay-Log Configuration of SMTP routes Here you have to set to which mail server a received mail should be forwarded. If this does not happen, the mail relay evaluates the MX record of the recipient domain - which points to the relay itself! A so-called "loopback" is then detected, which cancels the acceptance of the mail with a corresponding error message. In the following, further domains can be forwarded to the same or to other mail servers.
With the button + Add SMTP-Routing  further routes are created.

Required information:
Domain:	anyideas.de (or the corresponding mail domain)
Mailserver:	either as FQDN or the IP address

Settings

Settings

In this section you can configure the verification of the destination email address. It causes mails to unknown recipients to be rejected. On the one hand the attempt to deliver spam to "invented" recipients is effectively prevented, on the other hand legitimate senders receive feedback that their mail could not be delivered, for example because they have committed themselves to the recipient address.

Function	Option	Description
Email address validation:	Off	There is no verification of email addresses. An attempt is made to deliver all mails.
	SMTP	The Securepoint appliance queries the internal mail server in the background. notempty Hinweis The validation must also be active on the mail server! (Recipient Verification e.g. with an Exchange).
	LDAP	For example, the Securepoint appliance queries the Active Directory server. In the case of authentication via LDAP, the corresponding server must be configured under Authentication AD/LDAP Authentication . The user does not necessarily have to be the administrator, one user with read privileges is sufficient.
	Local email address list	Mail address list A list of accepted mail recipients can also be created locally.
Add email Address		This can be used to add mail addresses.

Signing

Signing

Outgoing emails can be signed using DKIM DomainKeys Identified Mail. The individual segments in the header and the body are signed separately, so that forwarding a mail via a mail server and changing the mail header does not destroy the signature.

General
Caption		Value	Description	Mailrelay UTMuser@firewall.name.fqdnApplications Mailrelay-Log Signing with DKIM
DKIM Sign		On	At activation, DKIM signing can be used.
Sign local email:		On	Mails originating from the UTM are signed with DKIM.
Maximum processes:		2	Controls global number of concurrent connections to mail relay (and attached filtering and anti-spam processes)
Domains
Add default configuration			Adds a default configuration. For this purpose, an RSA key is generated (Selector) and assigned to each mail domain entered as SMTP route
Add			Adds a domain name record
/			Opens / closes the overview that shows the selectors for a domain that are used for signing.
			Removes a selector from a domain entry
	Displays the DNS Settings
	Plain text	No	With Yes activation the DNS settings will be displayed in one window. If a separate authoritative DNS server is operated, this value can be copied directly into a BIND zone file.
	Subdomain		Copies the entry to the clipboard. To assign the subdomain at the DNS hoster.
	TXT Record		Copies the entry to the clipboard. To assign the subdomain at the DNS hoster. This is the public part of the RSA key, which must be stored in the TXT record of the mail domain. ‍ Can also be found in the menu Authentication / RSA keys / Public part (of the corresponding key) / PEM format
			Edits the respective domain name
			Deletes the entry
DKIM Selectors
Add			Adds a DKIM selector
			Adds the selector to the active (blue highlighted) domain entry.
	Edits the entry
	Name:	selector-2020-02-13-1	Name of the selector
	RSA Key:	Key name	Select existing key or create a new key pair with the button
	Hash algorithm:	sha256	Algorithm used
	[–] Advanced settings
	Email Header Canonicalization:	relaxed	Canonicalize the email headers. ‍ Since various sources (like relaying mailservers) might alter the email headers, it is possible to use a canonicalized version of those headers before creating the signature and also before validating it - the headers itself will stay unaffected. This will make the digital signing more reliable.
		simple	Do not canonicalize the email headers.
	Email Body Canonicalization:	relaxed	Remove trailing blank lines and cleanup whitespaces. ‍ Since various sources (like relaying mailservers) might alter the email body, it is possible to use a canonicalized version of the body before creating the signature and also before validating it - the body itself will stay unaffected. This will make the digital signing more reliable.
		simple	Remove trailing blank lines only.
	Sign default email headers:	Yes	Default: h=From:Reply-To:Subject:Date:To:Cc:Resent-Date:Resent-From:Resent-To:Resent-Cc:In-Reply-To:References:List-Id:List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; ‍ → RFC 6376 5.4.1
	Email headers to be signed:	»From »Date »Subject »To »List-Unsubscribe »List-ID	Email headers to be signed.

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Optional Settings

Further settings are recommended, but not mandatory for operative use:

Greylisting

Greylisting

Greylisting causes the delivery attempt of an unknown mail server to be initially rejected. Usually, spambots do not make any further delivery attempts, so that the delivery of spam was already successfully prevented before the mail had to run through the spam filter engine. A regular mail server, on the other hand, will make another successful delivery attempt after a certain period of time.
The following configurations are possible:

Allowlist Allowlist
Caption	Default	Description	Mailrelay UTMuser@firewall.name.fqdnApplications Mailrelay-Log Configuration of Greylisting
IP / Networks:	»10.0.0.0/8 »172.16.0.0/12 »192.168.0.0/16 »127.0.0.0/8	The default are the private IP address ranges and the loopback address. With a click into the clickobx you can add further networks and single hosts (e.g.:»203.0.113.113/32)
Domains:		Here single Mailserver domains can be added e.g.: smtp.anyideas.de The domain of the mail server does not have to be identical with the e-mail domain of the sender. Example: Sender user@ttt-point.de sends via the mail server »smtp.anyideas.de
Recipient:		Individual recipients can be added here, e.g: »MailUser@ttt-point.de
Sender:		Individual senders can be added here e.g.:{cb
Settings Settings
Greylisting:	Off	On activates the function. ‍ Delivery attempts from unknown mail servers are initially rejected.
SPF:	Off	If the Sender Policy Framework of the sender domain is correctly entered in the DNS, the mail will be delivered without delay if On is activated.
Add header:	Yes	By default, an additional greylisting entry is added for each recipient listed in the mail header. This can cause problems in case of many recipients. When disabled, no greylisting headers are inserted.
Automatic allowlisting for:	7 Days (Default)	For this period, after a successful delivery mails will be accepted immediately.
Delay:	2 Minutes (Default)	The period of time that the sending mail server is given to make another delivery attempt.
Subnet Match Subnet Match
Subnet mask IPv4:	»32	Instead of the sending server having to have the exact IP address as before, this can be changed so that, for example, only the first 2 or 3 octets have to match. This enables allowlisting even if the sender has several mail servers. Possible values: (Only one value can be entered.) »32 (Single Host) »24 Subnet, with match of first three octets »29 Any value via keyboard input.
Subnet mask IPv6:	»128

Depending on the configuration of the sending mail server, the re-delivery may be delayed by much more than the configured period (default 2 minutes) - in extreme cases by several hours. In this case, senders or recipients of particularly time-critical emails can be entered manually in a allowlist.

If a larger value for delay of e.g.: 30 minutes has been selected, the scan engine may have a higher probability of detection for new outbreaks when re-delivered with virus signatures that have been updated in the meantime.

Domain Mapping

Domain Mapping

Domain Mapping

Domains can be mapped to receive incoming mails to e.g. user@anyideas.net also under user@anyideas.de.

With Add Domain Mapping the mapping between two domains can be activated.

To do this, a Source-Domain: and a Destination Domain: must be specified.

Advanced Settings

Advanced

Here some further options to avoid spam can be found, each of which can be activated individually:

Greeting Pause
Caption	Function	Description	Advanced Mail Relay Settings
Status:	On	activates the function.
Duration:	2	Seconds (default value). Time the mail relay delays the greeting message. If the connected client sends SMTP commands before this time has elapsed, its request is rejected at the RCPT TO command with a "Protocol Error". Exceptions can be defined as network or host IP address for known mail servers. Successfully waiting mail servers are also automatically allowlisted for one day.
Recipient Restriction
Status:	Off
Limit:	25	Recipient
Restriction per client
Enable connection limits:	Off	Exceptions can be defined as network or host IP address for known mail servers. Configuration if a single mail server (identified by its IP address) is to establish a maximum of one connection to the UTM Appliance and a maximum of 5 connections per minute in succession:
Allowed connections:	1	Number of (client) connections, per connected mail server.
Enable rate control:	Off	Limits the number of (client) connections per connected mail server within a time frame.
Time frame:	60	seconds
Connections per time frame:	5
Others
HELO required:	On	Should absolutely remain activated (default). This switch exists to ensure backward compatibility.
Require reverse DNS lookup:	Off	Requires a reverse lookup (address) to exist for connected mail servers. The forward lookup must return the IP address.
Accept unresolvable domains:	Off	Allows sender addresses whose domain cannot be resolved via DNS.
Maximum processes:	10	Controls global number of concurrent connections to mail relay (and attached filtering and anti-spam processes)

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Configuration of the mailrelay for outgoing mails

To make sure that no spam or malware can be sent from your own network, the mail relay can also be used for outgoing mails.

Set of rules

To allow access to the mail relay, the hosts authorized to send mail must be allowed access to the corresponding interface of the Securepoint appliance (depending on the zone in which the hosts are located) via the SMTP protocol. Depending on the requirements, this can be a single host (e.g. the mail server), a group of hosts or the entire network. It is important that all applications that are to send mails via the mail relay have entered the corresponding firewall interface as SMTP server or smarthost. For example, to allow the internal network access to the mail relay, the set of rules can be created with the predefined network groups:

Packetfilter UTMuser@firewall.name.fqdnFirewall Update rules # Source: Destination: Service: NAT Action Active: 1 internet external-interface smtp Accept On 2 internal-network internal-interface smtp Accept On

Add network object UTMuser@firewall.name.fqdnFirewall Netzwerkobjekt Mailserver

If only the mail server is to be able to send mails, it must first be created as a network object:

This object can then be used in the firewall rule:			Packetfilter UTMuser@firewall.name.fqdnFirewall Update rules # Source: Destination: Service: NAT Action Active: 3 internet external-interface smtp Accept On 4 Mailserver internal-interface smtp Accept On -
Active:	On	Activate rule so that the portfilter takes effect
Source:	Mailserver	Select Mailserver (or the network object created above) as the source
Destination:	internal-interface	Select internal-interface as the destination
Service:	smtp	Select smtp as the service
Action:	Accept	Mails that meet the corresponding conditions are accepted and forwarded
Logging:	None - Do not log	Logging is not required
Group:	default	The portfilter rule can be assigned to a group

If a certain group of computers in the internal network is to be allowed to use the mail relay, these computers must be created as network objects. These can then be combined in a group (e.g. "SMTP Authorized").

Configuration Relaying

In order for the mailrelay to accept mails from the internal network or from the mail server, the settings in the

Relaying

} tab must be supplemented by a corresponding entry. The network address of the corresponding subnet or the IP address of the relevant computer serves as criterion:

+ Add Domain / Host

Domain:	192.0.2.0/30 or 192.0.2.192 notempty These are sample IPs for the internal mail servers. These have to be replaced by individual addresses!
Option:	None
Action:	Relay

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Conclusion

The UTM can now check incoming and outgoing mails for spam and viruses.