How to allow EAI - our solution

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The SMTPUTF8 Extension (rfc6531 3.2)


If SMTPUTF8 is not supported by receiving SMTP server – it Must Not transmit.  


  • Transform the Message
  • Reject the Message
  • Re queue later or try an alternate MX

Transform the Message

  • Transformation are outside the scope of the RFC. Thus we Apply a Filter on the MTA (same way as SpamAssassin/ClamAv works) before sending the mail to the outgoing/final queue.
  • Filter messages before sending
  • Test the Recipient if it supports SMTPUTF8 extension
  • Rewrite the User and Domain based on Mapping System/Mail Alias
  • Send the message normally