Hello ,
this is a great email client, i have a problem how do it makes my inbox and sent backup constanttly to a pst file , 

Hi Dan

eM Client does not use a pst file. Whereas Outlook stores everything in a single file, eM Client stores everything in a folder.

You can set the automatic backup of eM Client at Menu > Tools > Settings > General > Backup. You can specify where and when to back it up. This will then create a zip file of your profile folder.