Install libgmime-2.6-dev by entering the following commands in the terminal:
sudo apt update sudo apt install libgmime-2.6-dev
Description:
MIME message parser and creator 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 the development files of the older version of GMime for programmers using C or Vala. . It is recommended to use libgmime-3.0-dev instead of this package.
Homepage: https://github.com/jstedfast/gmime/
Version: 2.6.23+dfsg1-2
Section: universe/libdevel