Messages sent between accounts of same domain continuously was ended in junk folder. This is pretty bad because users connected with POP don't have the opportunity to see the Junk folder. So they couldn't see the important emails sent to them.
When look at messages headers we cant see any directive for deliver for junk, any spam score or anyting to cause dropping to junk folder.
"Mailenable Management>Servers>localhost>Extensions>Junk E-mail Processin" option was set already to "Messages are moved to Inbox"
During the tests we performed to repeat the problem, we noticed that the mail was moved to the Junk E-mail folder immediately after they drops into the inbox. After reviewing all relevant logs, in IMAP records we found that some strange IPs made this move after success authentication. First, we thought the accounts are compromised, until see same issue for different domains accounts.
All IPs we found were somehow related to my.com.
Immediately we blocked the IPs between 185.30.0.1 - 185.30.254.254 with the firewall. We did the tests again, and now we've seen that the e-mails normally fall into Inbox.
But after a few hours, our customers said they couldn't get e-mails on their phones. It turned out that they used an application called Mymail. We suggested that they uninstall the application and use another application for their mail.
I didn't have the chance to test the application, but I think it offers a spam management service. Propably when the application applies its own spam rules, it causes messages to be sent to the Junk folder.
I hope my explanations help those who have similar problems.
