503 5.7.0 encryption too weak 0 less than 128

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Article ID: 156999

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Updated On:

Products

Messaging Gateway

Issue/Introduction

You have set up a message to be sent requiring TLS but the message shows in the Message Audit Log as not delivered with the error "503 5.7.0 encryption too weak 0 less than 128"

Cause

The mail server you are trying to send to does not advertise the STARTTLS command

Resolution

This can be caused by multiple situations:

  • The recipient mail server's MTA does not support or has not been enable to advertise TLS.
  • A feature such as 'inspect esmpt' has been enabled on the local or remote firewall masking out the STARTTLS command.