Client "resets" often

Lately my eM client seems to ‘reset’?

My entire inbox will be cleared (not deleting anything) then it will proceed to receive my very large inbox from the beginning which will take a long time and popping up with email notifications all day of very old emails.

This has happened numerous times in the last month and it has become a very big issue for me.

What might be causing this as it needs to be fixed or I will be removing the client and using something else.

Well guess its time to uninstall, thanks for 2 years of good use but now cant use this software anymore.