Install libnotmuch5 by entering the following commands in the terminal:
sudo apt update sudo apt install libnotmuch5
thread-based email index, search and tagging (runtime)
Notmuch is a system for indexing, searching, reading, and tagging large collections of email messages in maildir or mh format. It uses the Xapian library to provide fast, full-text search with a very convenient search syntax. . This package contains the runtime library, necessary to run applications using libnotmuch.