Thunderbird is the powerful email client from Mozilla, with support for POP3 for keeping email locally and IMAP for remote storage. In addition, it features chat support, feeds reader and newsgroups. The interface is similar to the one of the newer versions of Firefox.

Evolution is the default GNOME email client and contacts organizer. Evolution Mail will display a wizard called the Evolution Account Assistant the first time it starts, where you can configure mail details like username, password and the protocol to use. It has features like tasks, calendar, memos and contacts.

Claws Mail is a powerful email client with support for POP3 and IMAP. You will have to specify the server address when creating a new email account (like pop.mail.yahoo.com and smtp.mail.yahoo.com for Yahoo!).

KMail is the powerful email client that ships by default with KDE. KMail detects the other email clients installed on the system and will allow you to import existing accounts from them.

Geary is a relatively new client with a simple interface which by default provides three vertical panels. It is not as feature-rich as the other, more powerful applications, but it will fit users who need a minimal interface. Geary supports the IMAP protocol.

Balsa supports POP3 and IMAP, and is written with GTK2. Balsa has a handful of features, ships with powerful configuration options and comes with a typical interface.

Since there are a lot of GTK-based clients, a client written in Qt should be a fresh breeze for KDE users. Trojita is written in Qt4, comes with a minimalist interface and features, and support for the IMAP protocol.

Amongst the many features the Opera browser comes with, an email client is also included. With support for IMAP and POP3, the mail client is opened in a new tab and it is divided in three vertical panels. For those who are using Opera as their main web browser, the Opera mail can be the right choice.