This is a fairly common issue when if there is a vacuum breaker under the sink that has a faulty spring.  This is the pipe that goes up just under the countertop and has a square box with a flat top ... they are inexpensive at most any hardware store and just screw on.  Normally you would get a sewage smell but in your case it must be the sulfur smell.  The other cause of a sulfur smell is usually the water heater ... you would smell the sulfur in the hot water and would indicate the heater needs to be flushed and anode rod replaced.  here is an Amazon add for a breaker: 

https://www.amazon.com/RecPro-Breaker-Protect-Pollutants-571-VAC-CHK/dp/B085CNLP9R/ref=asc_df_B085CNLP9R/?tag=hyprod-20&linkCode=df0&hvadid=692875362841&hvpos=&hvnetw=g&hvrand=17693981045436435886&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9006588&hvtargid=pla-2281435179098&psc=1&mcid=12b98fe6170c3a5c989adb00dede2734&hvocijid=17693981045436435886-B085CNLP9R-&hvexpln=73&gad_source=1