On a very basic level, DKIM is technology that looks at the sender’s domain (after the @ sign) and verifies to see if the email did, in fact, come from that domain. If it doesn’t match then there is a possibility that the email won’t go through or get flagged as potential spam.
On a deeper level, a digital signature is attached to each email. When it reaches the receiving party they check the signature by looking at two things in the email header (which normally most recipients don’t see): a private key, which is the signature of the sender and a public key, which verifies the hidden private key.
VerticalResponse uses a variety of these digital sending techniques, including DKIM, to make sure your email gets to the inbox.