Send emails securely, both with and without using Sikker@mail

Read on to find out when you need to use Sikker@mail and when you can just use your AU email.

All emails sent from AU's mail server are secured with encryption via a Force TLS (Transport Layer Security) solution. This also applies to emails sent via This significantly enhances email security.

In most cases, you can simply use your regular AU mail when sending emails to external recipients, but in some cases you still need to use the Sikker@mail solution.

Find out when below.

Can be sent via regular AU email

Confidential data such as:

  • Confidential data on one person to a maximum of five recipients.
  • Confidential data on five people to a maximum of one recipient.
  • CPR numbers
  • Employee home address, private email address, private telephone no. and other personal information
  • Personality tests
  • Marital status
  • Adoption details
  • Grades and grading

May not be sent via regular AU email

Confidential data, if it concerns:

  • Confidential data on more than five people
  • Confidential data to more than five recipients.

Sensitive data such as:

  • Race and ethnic origin
  • Political opinions, religious beliefs or philosophical beliefs
  • Trade union membership
  • Genetic data
  • Biometric data for unambiguous documentation
  • Health information
  • Sexual relationships or sexual orientation
  • Offences under Article 10.

If you are a system owner or researcher who processes sensitive data, you still need to conduct a risk assessment for how you exchange data. Read more about risk assessment.

Secure email - The Send Sikkert button

If you work with data that cannot be sent via regular email or if Force TLS does not meet your needs, you should use Sikker@mail.

With Sikker@mail, you can send confidential information and sensitive personal data via email. Sikker@mail encrypts and signs your email. Learn more here.

Important: If your email is rejected

In rare cases, emails may be rejected by the recipient's email system if it does not support Force TLS encryption.

When this happens, you will receive a Non-Delivery Report (NDR) as shown below. You then have the option of resending the email, but with the addition of one of the following tags in the subject field. The email will then be sent without TLS encryption.


  • [notencrypted]
  • [unencrypted].
  • [NoTLS]

We encourage you to use these tags only when absolutely necessary, as TLS encryption provides the highest level of security.

Please note that sending public data is only permitted if TLS is not used.

Non-Delivery Report (NDR) example

If a receiver does not support Force TLS, the following error message is received. See above how to send without TLS.

451 5.7.3 STARTTLS is required to send mail