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Split Delivery with Google Workspace

What is "Split Delivery"?

Split Delivery is a common technique used when two seperate Mailservers handle one signular E-Mail Domain.

Example: Mailserver 1 handles user@domain.com and Mailserver 2 handles servicemail@domain.com

What is required

  • Two seperate Mailservers (Google Workspace / G-Suite and Mailcow in this Case)
  • Access and Understanding to DNS Records
  • Understanding of DKIM/SPF
  • Understanding of Mail Routing Policies
  • Administrator Access to Mailcow
  • Administrator Access to Google Workspace Admin / Google Admin Console

1. Mailcow Configuration

  1. Open Mailcow Admin UI
  2. Go to System - Configuraiton
  3. Go to Options - Forwarding Hosts
  4. Add public Mailserver IPs from Google here
    • 108.177.16.0/24
    • 108.177.17.0/24
    • 142.250.220.0/24
    • 142.250.221.0/24
    • 2600:1901:101::0/126
    • 2600:1901:101::4/126
    • 2600:1901:101::8/126
    • 2600:1901:101::c/126
    • 2600:1901:101::10/126
    • 2600:1901:101::14/126
    • 209.85.128.0/17
    • 74.125.0.0/16
    • 66.249.80.0/20
    • 173.194.0.0/16
    • 64.233.160.0/19
    • 172.217.0.0/16

2. Google Configuration

This Part is in German, English Names might be slightly different

2.1 Configure Mailcow Forwarding Host

  1. Open Google Admin Console
  2. Go to Apps - Google-Workspace - Gmail
  3. Click Hosts
  4. Click Route hinzufügen
    • Set Name, Hostname and Port of your second Mailserver to which E-Mails will be forwarded to
    • Enable TLS requirements and Host check. While not necessary, it is recommended

2.2 Configure Mail List

This Step creates a fixed List of Mail Addresses that will be forwarded. Will this is not strictly necessary, its a absolute way to make sure they're being forwarded

  1. Open Google Admin Console
  2. Go to Apps - Google-Workspace - Gmail
  3. Click Routing
  4. Click Adresslisten verwalten
  5. Click Adressliste hinzufügen
    • Add all your Mail-Addresses
    • Uncheck Authentifizierung erforderlich

2.3 Add Route to Google

  1. Open Google Admin Console
  2. Go to Apps - Google-Workspace - Gmail
  3. Click Routing
  4. Click Routing-Regel hinzufügen
    1. Set Name
    2. Select Eingehend and Intern - Empfangen
    3. (Optional) Enable Benutzerdefinierten Betreff voranstellen and add [G-SUITE-RELAY]
    4. Enable Route ändern and select your Mailserver Host created in 2.1
    5. Click Optionen einblenden
    6. Select Unbekannte/Catchall Konten

 

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