Emails from same domain goes to trash

Hi, so I have this very wierd problem that I can't find a solution to. It started a while ago when a user (user1@domain.com) noticed that e-mails from another user (user2@domain.com) were going to trash. The wierd part is that this happens only between these two specific users when user2@domain.com sends an e-mail to user1@domain.com and NOT vice-versa. I tried placing email filters that would specifically deliver email from user2 to user1's inbox but it didnt change anything. Another thing to note is that when I manually move the e-mails to inbox, after a while they are moved automatically to trash. I'd appreciate some help as I don't have any idea anymore. Thanks in advance,