DomainKeys Identified Mail
DomainKeys Identified Mail (DKIM) is a protocol for signing outgoing email
messages with a signature that proves it really comes from the sender's
domain. This can be used by recipient mail servers or spam filters to detect
sender forgery, which is typically done by spammers to avoid having their
domain blacklisted.
When DKIM is enabled using Virtualmin your mail server will be configured
to add a DKIM signature to all outgoing messages, and a public key will be
added to each of the DNS domains on your system. Other mail servers can then
use this key to verify the signature on relayed messages, thus ensuring that
the sender's address was not forged.