Support for 2048-bit keys for DKIM configuration

DomainKeys Identified Mail (DKIM) is a cryptographic technology that uses a public key and a private key to verify that the sender of the email is responsible for the corresponding domain. DKIM is a way for valid email senders to prove themselves legitimate. For a long time the standard key length was 1024 bit DKIM keys, but threat actors continue to develop new methods to break DKIM keys. As a result, the National Institute of Standards and Technology (NIST) recommends 2048-bit keys.