Error: "451 TLS/SSLv3 Connection required. (#4.7.1)"
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Error: "451 TLS/SSLv3 Connection required. (#4.7.1)"


Article ID: 162152


Updated On:




You are sending to a domain protected by the Symantec Email service, or you are a customer subscribed to Symantec Email sending outbound through the service. The Email server responds to the SMTP RCPT TO: command with "451 TLS/SSLv3 Connection required. (#4.7.1)".

  • 451 TLS/SSLv3 Connection required. (#4.7.1)
  • Within the ClientNet portal, the Email Track and Trace tool shows "Not Delivered" in the Delivered column and "Boundary Encryption" in the "Service" column.


Symantec Email Security.Cloud Encryption


A TLS enforcement is configured on the Symantec Email protected domain account. If conducting a search on the portal section

Dashboard > Services > Email Services > Encryption

the 3rd party domain is listed on the TLS Business Partners, this indicates a TLS connection must be used when sending emails to and from the domain(s) in question.


The sending domain must configure its mail server so that it initiates a TLS connection to the recipient domain's mail server.