Install libopendkim11 by entering the following commands in the terminal:
sudo apt update sudo apt install libopendkim11
Library for signing and verifying DomainKeys Identified Mail signatures
The OpenDKIM Project is a community effort to develop and maintain a C library for producing DKIM-aware applications and an open source milter for providing DomainKeys Identified Mail (DKIM) service. . This package provides library for implementing signing and verification of the DomainKeys Identified Mail (DKIM) standard. This library provides support for signing and verifying signatures according to RFC 4871, and supports both DomainKeys signing policy and DKIM ADSP.