This is a follow up to the following questions about m-dissipativity:
Are m-dissipative operators closed?
Are m-dissipative operators closed (II)?
Is a dissipative closed operator $A:D(A)\subset X\rightarrow X$ in the Hilbert space $X$ maximal dissipative?
The answer is No. For maximal dissipativity we need $A$ dissipative and the range of $\lambda I -A$ should coincide with $X$ for some $\lambda>0$. This is the case if $0$ is in the resolvent set of $A$, i.e. if $A$ is a closed and boundedly invertible operator.
Requiring closedness results in the range of $\lambda I -A$ being a subset of $X$.