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Allow only authorized SMTP servers to communicate with your mail server

10/14/2021 30 People found this article helpful 148,940 Views

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    Description

    This article describes how to block all traffic from the WAN to a SMTP Server on the LAN or DMZ, except a range of IP Addresses on the WAN. This requirement usually arises when the user has a managed or hosted Spam Filtering service (eg. Postini) on the WAN and wishes to lock-down his incoming email to that service.

    Image

    Resolution

     

    Resolution for SonicOS 6.5

    This release includes significant user interface changes and many new features that are different from the SonicOS 6.2 and earlier firmware. The below resolution is for customers using SonicOS 6.5 firmware.

    Crating an Address Object for the IP Addresses of the hosted service: 

    • Login to the SonicWall management interface.
    • Navigate to Manage | Policies | Address Objects.
    • Create a new Address Object with following values.

      Name: Postini Network
      Zone: WAN 
      Type: Network (This could be changed to Range or Host as required)
      Network:  207.126.144.0
       Netmask:  255.255.240.0
      Image

    • Creating an Address Object for the WAN IP Address of the Mail Server with following values.

      Name: Mail Server Public
      Zone: WAN 
      Type: Host
      IP Address: 1.1.1.2
      Image

    • Creating an Address Object for the LAN (or DMZ) IP Address of the Mail Server with following values.

      Name: Mail Server Private
      Zone: LAN  (This could be changed to the zone of the Mail Server)
      Type: Host
      IP Address: 192.168.1.2
      Image

    Creating a WAN to LAN or DMZ allow rule:

    • Navigate to the Manage | Policies | Rules | Access Rules page.
    • Select From  WAN  To  LAN (This could be changed to the zone of the Mail Server).
    • Add the following Allow Rule.

      Action: Allow
      Service: SMTP
      Source: Positini Network
      Destination: Mail Server Public
      Image

    Creating a NAT Policy

    • Navigate to the Manage | Policies | Rules | NAT Policies page.
    • Create a new NAT Policy with following values.

      Original Source: Positini Network
      Translated Original: Original
      Original Destination: Mail Server Public
      Translated Destination: Mail Server Private
      Original Service: SMTP
      Translated Service: Original
      Inbound Interface: X1
      Outbound Interface: Any
    • Check Create a reflexive policy: This will create an outbound NAT Policy with Original Source as the private IP and the Translated Source as the public IP of the mail server.
      Image

    How to Test

    From a computer on the Internet try to telnet on port 25 to the public ip address of the Mail Server and it should fail. Likewise, try sending a mail and you should be able to receive it.


    Resolution for SonicOS 6.2 and Below

    The below resolution is for customers using SonicOS 6.2 and earlier firmware. For firewalls that are generation 6 and newer we suggest to upgrade to the latest general release of SonicOS 6.5 firmware.

    Crating an Address Object for the IP Addresses of the hosted service

    • Login to the SonicWall management interface.
    • Navigate to Network | Address Objects.
    • Create a new Address Object with following values.

      Name: Postini Network
      Zone: WAN
      Type: Network (This could be changed to Range or Host as required)
      Network:  207.126.144.0
       Netmask:  255.255.240.0
      Image

    • Creating an Address Object for the WAN IP Address of the Mail Server with following values.

      Name: Mail Server Public
      Zone: WAN 
      Type: Host
      IP Address: 1.1.1.2
      Image

    • Creating an Address Object for the LAN (or DMZ) IP Address of the Mail Server with following values.

      Name: Mail Server Private
      Zone: LAN  (This could be changed to the zone of the Mail Server)
      Type: Host
      IP Address: 192.168.1.2
      Image

    Creating a WAN to LAN or DMZ allow rule

    • Navigate to the Firewall | Access Rules page.
    • Select From  WAN  To  LAN (This could be changed to the zone of the Mail Server).
    • Add the following Allow Rule.

      Action: Allow
      Service: SMTP
      Source: Positini Network
      Destination: Mail Server Public
      Image

    Creating a NAT Policy

    • Navigate to the Network | NAT Policies page.
    • Create a new NAT Policy with following values.

      Original Source: Positini Network
      Translated Original: Original
      Original Destination: Mail Server Public
      Translated Destination: Mail Server Private
      Original Service: SMTP
      Translated Service: Original
      Inbound Interface: X1
      Outbound Interface: Any
    • Check Create a reflexive policy: This will create an outbound NAT Policy with Original Source as the private IP and the Translated Source as the public IP of the mail server.
      Image 

    How to Test

    From a computer on the Internet try to telnet on port 25 to the public ip address of the Mail Server and it should fail. Likewise, try sending a mail and you should be able to receive it.

    Related Articles

    • Troubleshooting Network throughput, Latency, and Bandwidth Issues with a SonicWall UTM
    • DHCP server packet dropped, RPF check failed
    • How to Block Facebook Apps using Application Control

    Categories

    • Firewalls > NSa Series > Networking
    • Firewalls > NSv Series > Networking
    • Firewalls > TZ Series > Networking

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