[Mixalis]

Further... I have tried sending from one mail account to the other but get the same result. The problem seems to be connected with sending from the iPhone, irrespective of which address I use. My @me account is set up on the iPhone as default, so I particularly wish to use this for sending. My other main service, @gmx, rejects the me+omnifocus address as invalid, so I'm back to sending from @me to @me. It ought to work...