Install libgmime2.6-cil-dev by entering the following commands in the terminal:
sudo apt update sudo apt install libgmime2.6-cil-dev
Description:
CLI binding for the GMime library (old 2.6 version) -- development files
GMime provides a core library and set of utilities which may be used for the creation and parsing of messages using the Multipurpose Internet Mail Extension (MIME). . This package contains development files for the older version of the gmime-sharp library, and should be used for compilation. . This package is deprecated. Users should switch to MimeKit instead.
Homepage: https://github.com/jstedfast/gmime/
Version: 2.6.23+dfsg1-2
Section: universe/cli-mono