astroid is described as 'Astroid is a Mail User Agent. As such, all Astroid provides is a graphical interface to your email. Thus, Astroid enables you to launch actions that rely on the performance of other programs to actually fetch, sync, index, search and send your email' and is an app in the OS & Utilities category. There are seven alternatives to astroid for Linux, Mac, Windows, BSD and Xfce. The best alternative is Mutt, which is both free and Open Source. Other great apps like astroid are aerc (Free, Open Source), notmuch (Free, Open Source), Nmzmail (Free, Open Source) and mu (Free, Open Source).
Notmuch is a system for indexing, searching, reading, and tagging large collections of email messages. It uses the Xapian library to provide fast, full-text search of very large collection of email with a very convenient search syntax.
Sup is a console-based email client for people with a lot of email. It supports tagging, very fast full-text search, automatic contact- list management, custom code insertion via a hook system, and more.