DKIM (DomainKeys Identified Mail) describes a method to verify the authenticity of an email sender system. In other words: was the email from person_X@companydomain.tld actually sent from companydomain.tld?
For this to work, the email is signed by the sender’s email system (asymmetric encryption private/public). The recipient can then verify the authenticity of the sender’s email system using a public key. The public key is published as a TXT extension in the domain’s DNS record.
This rather simple verification increases trust, especially with known communication participants, as it can quickly expose a crude sender forgery (From: field); however, it should always be ensured that the email (including the sender domain) appears known/trustworthy. This is because even malicious emails can be certified with DKIM (if the domain is managed by fraudsters).
Example:
- Mail From: eBay, Subject: Update your login credentials
- DKIM display in Thunderbird: DKIM valid (signed by phishing.anonymous-domain.com)
Although the DKIM check indicates a correct DKIM signature, it is to be expected that eBay does not send its emails from a domain named “phishing.anonymous-domain.com”..
Here is the link to the add-on page in the Mozilla Repository:
https://addons.mozilla.org/de/thunderbird/addon/dkim-verifier/