Yes, the Dashboard is currently limited to 40,000 entries, but this can be changed by creating the following registry entry:
Browse to HKLM\SOFTWARE\GFI\MailEssentials\EmailSecurity\Config (For 64bit systems, browse to HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\GFI\MailEssentials\EmailSecurity\Config)
Create a string value and name it logsfdblimit
Enter the desired limit
Restart the GFI MailEssentials services for the change to take effect
Note that the default limit of 40,000 is set to provide a balance between speed of the UI and the usefulness of data. The limit for what can be used while still maintaining a responsive UI will change depending on the speed of the server.