Suppose that is an algebra, σ, τ : → are two linear mappings such that both σ() and τ() are subalgebras of and 𝒳 is a (τ(), σ())-bimodule. A linear mapping D : → 𝒳 is called a (σ, τ)-derivation if D(ab) = D(a) · σ(b) + τ(a) · D(b) (a, b ∈ ). A (σ, τ)-derivation D is called a (σ, τ)-inner derivation if there exists an x ∈ 𝒳 such that D is of the form either or . A Banach algebra is called (σ, τ)-amenable if every (σ, τ)-derivation from into a dual Banach (τ(), σ())-bimodule is (σ, τ)-inner.
Studying some general algebraic aspects of (σ, τ)-derivations, we investigate the relation between the amenability and the (σ, τ)-amenability of Banach algebras in the case where σ, τ are homomorphisms. We prove that if 𝔄 is a C*-algebra and σ, τ are *-homomorphisms with ker(σ) = ker(τ), then 𝔄 is (σ, τ)-amenable if and only if σ(𝔄) is amenable.