synology NAS DS1019+ Mail Station setup

I made setup with Mail station on synology NAS as email backup server.
it was working with pop3 setup retrieving emails from email server,
but since few days ago, mail station pop3 function doesn’t work, it doesn’t take any emails from email server.
I guess i did something wrong while I made some changes on user detail or smtp setting.
if you have knowledge about mailstation, we can work together.