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The core idea behind this add-on is to allow one to be sure that a certain e-mail can be trusted.
This is mainly done by local verification of DKIM-Signatures in an e-mail. Though by now it has grown to include some other feature that help with that core idea.
Tip
It is helpful to keep in mind that the idea of this add-on is not to detect spam, i.e. helping you to find the bad e-mails. Instead it approaches the problem form the other way, helping you in being able to trust the legitimate e-mails you receive.
This may seem to be the same at first glance. It is however a different mindset that influences how this add-on works.
Below is a list of the main features of the add-on.
A complete description of all the available add-on options can be found at https://github.com/lieser/dkim_verifier/wiki/Options.
DomainKeys Identified Mail (DKIM) is a method which allows domains to sign e-mails. The add-on can locally verify these DKIM signatures and shows the result in the e-mail header. This way it is possible to see which domain is claiming responsibility for a specific e-mail.
Important
It is important to note that an e-mail can be signed by an arbitrary domain. A valid DKIM signature alone is therefore not an indicator for a trustworthy e-mail. Always check who the signer is to determine if an e-mail is trustworthy!
In some cases, the absence of a DKIM signature can be useful to identify scam e-mails. If it is known that a certain domain is signing all its e-mails with DKIM, the absence of a DKIM signature is a strong indicator for a forged e-mail.
Note
The DKIM verification is done according to RFC 6376, including the updates done by RFC 8301 and RFC 8463.
The Authentication-Results header (ARH) is a way for an e-mail server to record results of e-mail authentication checks that it carried out.
If enabled the add-on supports reading the following authentication checks from the ARH:
- DKIM
- SPF
- DMARC
-
Brand Indicators for Message Identification (BIMI)
- This is used to potentially show the brand icon before the From address.
Some may want the results of the add-on to be more prominently shown. Others want the add-on to keep more in the background.
Instead of forcing one or the other way onto you it allows you to change how the result is shown in various ways.
One of the highlights is the possibility to show the favicon of certain trusted signing domains
for easy trust recognition.
If you are interested in all the details of the DKIM signatures, the popup of the DKIM button in the e-mail header shows them. It will also show all DKIM signatures in the e-mail.
To ease the checking of if and by who an e-mail is signed, the add-on supports the use of sign rules. With sign rules it is possible to specify that e-mails from a certain sender have to be always signed by a specific domain (also referred to as SDID). More about sign rules at https://github.com/lieser/dkim_verifier/wiki/Sign-rules.
The add-on can be downloaded from https://addons.thunderbird.net/thunderbird/addon/dkim-verifier/ or https://github.com/lieser/dkim_verifier/releases. The source code is available at https://github.com/lieser/dkim_verifier
Support is given at https://github.com/lieser/dkim_verifier/issues or by e-mail to lieser+dkim@posteo.net (in English or German).
The preferred way to report bugs is by creating an issue at https://github.com/lieser/dkim_verifier/issues.
If debug information is needed, enabling of debugging in the advanced options is sufficient in most cases. Details about the available debug options can be found here.