It is quite lightweight. Takes 1/2 of Thunderbird`s RAM. It has a sound alert function in its filters section which is vital for me after the Mail Alert addon stopped working in Thunderbird after I moved from the X86 to the X64 system. The bad thing about it is that it permanently deletes messages when you delete them with Delete. To preserve deleted messages you need to move them by hand with the Move to function in the right-click menu. I can make a workaround for this disfunction with Autohotkey.