We consider the Moore-Gibson-Thompson equation with memory of type IIwhere A is a strictly positive selfadjoint linear operator (bounded or unbounded) and α, β, γ > 0 satisfy the relation γ ≤ αβ. First, we prove a well-posedness result without requiring any restriction on the total mass ̺ of g. Then we show that it is always possible to find memory kernels g, complying with the usual mass restriction ̺ < β, such that the equation admits solutions with energy growing exponentially fast. In particular, this provides the answer to a question raised in [2].2000 Mathematics Subject Classification. 35B35, 35G05, 45D05.