Installation Guide:

  1. How to Setup Postfix/DKIM/SPF on Ubuntu with or without Plesk Onyx
  2. How to setup DKIM/SPF/DMARC in Ubuntu with Plesk Onyx
  3. How to setup SPF (Sender Policy Framework)
  4. How to setup DMARC and Benefits
  5. Generate a public and private key from OpenSSL (if require)
  6. How to install/setup dkim in cPanel
  7. Server Speedtest from command
  8. User unknown in virtual alias table

Important Tools

For DKIM Checker: Read more