DomainKeys Identified Mail (DKIM) is a protocol allowing for email authentication utilizing PKI. Where does DKIM store its public certificate keys?

DomainKeys Identified Mail (DKIM) is a protocol allowing for email authentication utilizing PKI. Where does DKIM store its public certificate keys?

• Certificate authority
• MTA
• Mail server
• DNS

 

EXPLANATION

Somebody already did a very good summary of DKIM here:
https://blog.returnpath.com/how-to-explain-dkim-in-plain-english-2/
As a summary:

What it is: DomainKeys Identified Mail (DKIM) is a protocol that allows an organization to take responsibility for transmitting a message in a way that can be verified by mailbox providers. This verification is made possible through cryptographic authentication.
How it works: DKIM is pretty complicated. There are a lot of steps. Below, we’ll break them down as simply as possible.
Step 1: Identifying what message elements to sign with DKIM
Step 2: The encryption process
Step 3: Validating the DKIM signature with a public key

SOURCE

https://blog.returnpath.com/how-to-explain-dkim-in-plain-english-2/