The requirements towards marine fuel are listed in the DIN ISO 8217 –and were adopted directly out of the standard of the International Standardization Organization.* Maybe they should not have done this.
The DIN ISO 8217 splits marine fuels into distillates and residual oils, which are splitted into some more.
There are limits to all necessary product properties (density, viscosity, flash point). But not for sulphur content of residual oils.
Whereas, there are limits for the sulphur content of distillate oils which are impractical.