We consider a general matrix iterative method of the type Xk+1=Xkp(AXk) for computing an outer inverse f2ceea9237347ad">, for given matrices A∈Cm×n and G∈Cn×m such that AR(G)⊕N(G)=Cm. Here fff2bf190c630f307eba20d8" title="Click to view the MathML source">p(x) is an arbitrary polynomial of degree d. The convergence of the method is proven under certain necessary conditions and the characterization of all methods having order 2cdc880214377f9cde2d0ac9aaf70b0" title="Click to view the MathML source">r is given. The obtained results provide a direct generalization of all known iterative methods of the same type. Moreover, we introduce one new method and show a procedure how to improve the convergence order of existing methods. This procedure is demonstrated on one concrete method and the improvement is confirmed by numerical examples.