Thunderbird:
Thunderbird is an open source email client developed by the Mozilla open source community and easy to configure. The version of Thunderbird available for Windows 7 and 8 as well as for Linux, MacOS and other operating systems.
Features of Thunderbird:
It supports LDAP Email Address autocomplete. If an email was sent previously to the recipient or if the recipient is in your contact list, you can type just the first few letters of the person’s name, then the LDAP feature will complete the rest of the address. The unique feature of Thunderbird is a chat feature that enables you to converse with users on Facebook Chat, Google Talk, IRC, Twitter, and XMPP right from the application. Thunderbird includes a user-friendly contacts list, the application does not include a calendar or task list functionality by default. When installing extensions, it can provide both calendar and task list support, in particular, the popular Lightning calendar based on the open iCal standard.
Outlook:
Microsoft Outlook is a versatile email client. Microsoft Outlook has calendar and task tracking features. It is not an open source, therefore, the application is not free. Outlook is simple to set up with auto-discovery, but even if you must manually configure the software, the setup process is driven by a wizard. Additionally, you can configure complex rules to manage your messages and automate workflow, a feature that is not supported in Thunderbird.
Choose an email client based on your needs. If you need a secure business email client, then choose Microsoft Office applications. However, if you prefer open source software that is easy to set up and use, Thunderbird is a viable option.