Given a frequency λ = (λ n ) and ℓ ≥ 0, we introduce the scale of Banach spaces H λ ∞,ℓ [Re > 0] of holomorphic functions f on the right half-plane [Re > 0], which satisfy (A) the growth condition |f (s)| = O((1 + |s|) ℓ ), and (B) are such that they on some open subset and for some m ≥ 0 coincide with the pointwise limit (as x → ∞) of the so-called (λ, m)-Riesz means λn 0of some λ-Dirichlet series a n e −λns . Reformulated in our terminology, an important result of M. Riesz shows that in this case the function f for every k > ℓ is the pointwise limit of the (λ, k)-Riesz means of D.Our main contribution is an extension -showing that 'after translation' every bounded set in H λ ∞,ℓ [Re > 0] is uniformly approximable by all its (λ, k)-Riesz means of order k > ℓ. This follows from an appropriate maximal theorem, which in fact turns out to be at the very heart of a seemingly interesting structure theory of the Banach spacesℓ [Re > 0] basically consists of those holomorphic functions on [Re > 0], which fulfill the growth condition |f (s)| = O((1 + |s|) ℓ ) and are of finite uniform order on all abscissas [Re = σ], σ > 0.To establish all this and more, we need to reorganize (and to improve) various aspects and keystones of the classical theory of Riesz summability of general Dirichlet series as invented by Hardy and M. Riesz. DEFANT, SCHOOLMANN, AND ANDREAS DEFANT AND INGO SCHOOLMANN 4.1. Ordinary and power case 29 4.2. Perron formula -a variant 30 4.3. A maximal inequality for Riesz means 31 4.4. Uniform Riesz approximation 32 4.5. Theorem 41 of M. Riesz revisted 33 4.6. The bounded case ℓ = 0 34 4.7. Boundedness of coefficient functionals 34 4.8. A Montel theorem 35 4.9. Completeness 36 4.10. Behavior far left 37 4.11. Behavior far right 37 4.12. Finite order 39 4.13. Equivalence 40 References 44