DKIM (Domain Keys Identified Mail) is an email authentication technique that allows the receiver to check that an email was sent and authorised by the correct email account, and wasn’t modified in transit.
This is done by generating a digital signature (DKIM signature) for the email. This signature is encrypted and added to the message. If the email is altered between the time that it is sent and received, the signature will no longer match. The email server receiving your email can check the signature in the email, and reject the email if it doesn’t contain exactly the right signature.
DKIM is activated by default on Mumbai Hosting´s Servers.