Why do my emails in my inbox disappear after one week?

I got a new computer and am using eM Client on it for my emails.  I installed it in mid November and the emails I imported from old computer are still there but new emails are only in eM client are only there for a week and disappear.  I was used to having my emails on my computer until I deleted them.  Lots of important things vanish after a week.  I am sure I have something set up wrong but don’t know what.  I cannot find them in inbox or any other folder. 

check your archive folder   Did you set auto archive on ?   
Menu / Tools /Settings/  mail/archive

If automatic archive is not the reason, then it could be caused by another device connecting to the same account. 

Most likely eM Client is connecting to the account using IMAP and another device is connecting using POP3, which usually removes the messages from the server after one week.