Unfortunately, the posted thread doesn't answer the question. All programs both factory installed and my own downloaded Apps other than AquaMail read and write to my microSD card. And while AquaMail allows me to choose the extSD card and even a folder on the extSD card it refuses to download attachments anywhere but the internal memory simulated card 0.
I don't believe this is a Android problem but something not properly set up in AquaMail. However, I could be wrong - after all I have been wrong before.