I started the investigation on the two major email clients, i.e., Mozilla Thunderbird and Microsoft Outlook, today. The purpose of this investigation is to establish the technical basis on email projects. I usually use Thunderbird for reading my mails, so I prefer developing an add-on for Thunderbird in the first project. However, it seems to be easier to develop an add-on for Outlook. So I will investigate both and decide which one to use first.