Email penetration tests: How secure is your email security?

A black box penetration test simulates the perspective of an external attacker who has no internal knowledge of the organization. The testers only have access to publicly available information, such as the domain or mail servers that can be accessed from outside.

The goal is to find out which vulnerabilities an attacker without any special prior knowledge could exploit. To do this, the mail server ports are scanned, the MX records and DNS entries are analyzed, and the authentication and encryption mechanisms are checked, among other things.

Typical checks include whether emails can be forged in the name of the domain, whether the server can be misused as an open relay, or whether there are faulty configurations in SPF, DKIM, or DMARC. The depth of these tests is limited, but that is precisely why the results are very realistic.

A gray box penetration test combines the external perspective of an attacker with a limited amount of internal knowledge or access data. For example, testers have a standard user account, internal email addresses, or basic information about the infrastructure used. This allows them to more specifically test how a semi-informed attacker—such as an employee with malicious intentions—might proceed.

In practice, not only external protection mechanisms such as SPF, DKIM, and DMARC are tested, but also internal security measures: For example, tests are carried out to see whether emails can be manipulated within the company, whether malicious attachments are detected by internal filters, and how well employees respond to phishing campaigns. The grey box approach enables a more realistic assessment of overall security, as it takes into account both the technology and the behavior of the workforce.

A white box penetration test provides the most detailed analysis, as testers gain complete insight into the company’s email infrastructure, configurations, and security policies. All technical and organizational aspects are reviewed, including server and gateway configuration, encryption and authentication procedures, and incident response processes.

Typical tests include detailed checks on how security mechanisms can be circumvented, whether logging and monitoring are sufficient, and whether vulnerabilities can be exploited in practice. White box tests often also involve phishing campaigns with individual scenarios to assess the organization’s responsiveness.