In terms of security also, Outlook has better anti-spams, anti-virus and password protection functionalities. It shows un-matching compatibility to IMAP and Exchange Server, mobile platforms, which Thunderbird lacks. Outlook is an advanced, popular email client which allows its users to work offline also. Many organizations are trusting trust the Outlook client for long term use as if we make comparisons of the both the email clients, then Outlook email client would outstands definitely. Switching from MBOX email clients like Mozilla Thunderbird to Microsoft Outlook is trending from a long time.
