Siebe asked: “Where do those dhamma come from that are detected by the mana indriya?”
Just like visual signals come to the physical eyes from the external world, dhammā come to the mana indriya from the external world.
– But unlike visual things (trees, people, etc), dhammā cannot be “seen” or “touched” (dhammā are: anidassanam, appatigham dhammayatana pariyapanna rupam).
– Dhamma are in the immaterial world, compared to rupa in the material world. See, “Our Two Worlds: Material and Immaterial.”
“Do i understand it correctly, that when there is no mana indriya in a gandhabba that has left the body, there are also no memories in this gandhabba?”
Gandhabba does not have eyes but can see. In the same way, gandhabba does not have a mana indriya but can receive dhammā.
– It is only when a gandhabba is inside a physical body that it needs those six indriya to receive external rupa and dhammā.
You may need to go through the relevant posts again to get the idea. Here si another relevant post: “Citta and Cetasika – How Vinnana (Consciousness) Arises.”
Dhamma are rupa below the suddhatthaka stage: “What are Rūpa? – Dhammā are Rūpa too!.”