Incoming mail is not received without any errors in logs.
When source mail address is blacklisted the message is silently dropped.
Check Black List for patterns that might match incoming mail address in Plesk->Tools & Settings > Mail Server Settings->Black List. For clarity enable Plesk debug and check log/event viewer for messages such as this one. Example from Windows event viewer:
Received message from (firstname.lastname@example.org) - bad mail, mask(*mail.com) Execute file name: C:\Program Files (x86)\Parallels\Plesk\admin\bin\plesksrv.exe