Mozilla Thunderbird: This program is a sand-alone mail client which used to form part of Mozilla's Application Suite. It is excellent and very effective in such things as junk mail identification filter, anti-phishing protection, security, and automatic updates. Since its code is free, under the same licenses as Fireox, it is being developed by a community. Now, setting up as a mail client is extremely easy, since it has a mail account setup wizard. Mozilla made it easy to add new e-mails to your address book, and it has an activity manager to know what is happening with your email.
It is convenient to use it along with the GNU Privacy Guard (GnuPG), a free implementation of OpenPGP, and lets people encrypt or sign digitally data communication. For Windows users, Gpg4win is a graphical frontend for GnuPG, and helps to generate key encryption. The program which lets Thunderbird interact with GnuPG is called Enigmail, which makes key-creation and e-mail encryption extremely easy.
|Kontact: It is a Personal information manager, which includes KMail as an email client. it is very efficient, very easy to set up, although not as easy as Thunderbird or Spicebird. What makes it so great is that it integrates an addressbook, a notebook, a usenet mail reader, a calendar and scheduler, and even a program to track how much time you spend in tasks. I've used it for a long time before Spicebird, and I highly recommend it.|