Lexmark MS621
This article contains instructions on how to adjust print resolution to reduce graininess or coarseness.
Check if the printer is using a genuine and supported toner cartridge and print the document.
Note: If the cartridge is not supported, install a supported one.
Depending on your operating system, specify the print resolution from the Printing Preferences or Print dialog.
Set the resolution to 600 dpi.
Print the document.