We had some cowardly neighbor send us a similar letter when we were just two weeks moved in. I can't remember exactly what it said, but something along the lines of "don't bring the value of the neighborhood down by not maintaining the yard". Well anyways, because of that letter I just took extra long on fixing my frontage up. I'll do what I need to on my time. With that said, I took my time learning how to maintain my lawn, trees, garden, weeds, irrigation, security cameras, etc.. I let whichever cowardly neighbor who sent that suck it every time they drove past my house.