In this article, we will take a look at how to enable explicit DKIM signing in Office 365.
What exactly is DKIM?
DomainKeys Identified Mail (DKIM) is an email authentication mechanism designed to prevent email spoofing. DKIM utilizes a cryptographic key pair and DNS records to provide sender validation and message integrity. It does this in the following way.
The sender encrypts selected parts of the message header with its private key. This is defined by the “h” field in the diagram above. In our example, we are encrypting the From, To, and Subject fields to name a few. Portions or all of the message body may also be hashed. The DKIM header itself is not encrypted. In the DKIM header, the “d” value identifies the sender domain. The “s” value identifies a unique selector defined by the sender.
The recipient combines the selector and domain values to form a DNS query. Using our diagram above the domain field is marked as supertekboy.com and the selector field is marked as selector1. Using these values the recipient forms the following DNS query.
The _domainkey portion of the query is a fixed part of the protocol.
The name servers for the sender respond with a TXT record containing the public key. The recipient can then use this public key to decrypt the header (and any parts of the body).
Successful decryption validates the sender. A DKIM=Pass is attached to the message header which increases the confidence level of the message.
One of the drawbacks of DKIM is that it doesn’t prevent close misspellings of a domain. For example, I could register supertecboy.com and configure DKIM signing. DKIM will pass because the messages are coming from supertecboy.com. But to an untrained eye, supertekboy.com and supertecboy.com might be considered the same entity. When in fact the latter is a spoofer.[Read more…] about Enable explicit DKIM signing in Office 365