451 Requested action aborted Reject due to policy restrictions

Reason

Your email has been temporarily rejected by our systems because it has a high similarity with spam messages.

Solution

If you are responsible for the sending infrastructure, please check your systems to ensure that no spam is sent and that they are protected against unauthorized access.

You can positively influence deliverability by DKIM signing your emails. The DKIM signing domain should match your From domain (RFC 5322.From) in order to achieve DKIM alignment.

Below you will find examples that illustrate this requirement:

Example 1 (relaxed DKIM alignment)

DKIM Domain: example.com
From Domain(RFC 5322.From): child.example.com

Example 2 (relaxed DKIM alignment)

DKIM Domain: child.example.com
From Domain(RFC 5322.From): example.com

Example 3 (strict DKIM alignment)

DKIM Domain: example.com
From Domain(RFC 5322.From): example.com

Example 4 (strict DKIM alignment)

DKIM Domain: child.example.com
From Domain(RFC 5322.From): child.example.com

If your emails are already signed and you assume that they have been misclassified by our systems, you can contact us using the following form.

If possible, please provide us with all helpful information for processing, such as

complete error message
DKIM domain you use to sign your emails
IP addresses, IP ranges (CIDR), AS

Name

Email address

Company (optional)

Message (optional)