Notifications regarding installed updates are sent by Parallels Plesk Panel (Plesk), even if there are no updates installed. For example:
Attention, Parallels Panel was successfully updated. To view the list of changes, visit http://download1.parallels.com/Plesk/PP11/whatsnew-redirect.htm?platform=unix&locale=en-US&version=11.5.30. This message was sent automatically by Parallels Installer.
This issue is caused by a product bug (an internal issue with the ID PPPM-837).
The issue has been permanently fixed for Linux in Plesk 11.5.30 Micro-Update #18. Update to the latest release in order to resolve the issue.