Problem mailbox always almost move mail ( from internal user A to(to, CC or BCC) problem mailbox ) to junk box. Not only newly received but also mails manually moved to inbox from junk.
Set spam filter to off or high or low in both OWA and Outlook on windows.
But nothing found. Tried to check audit log for problem mailbox which LogonTypes is Owner and Operation is Move but shows nothing (Maybe something wrong here cause manually move mail from junk to inbox should be logged but no).