I booked RDU-IAD-SFO-IAD-RDU and it came up as booked in "E" -- which according to my (possibly old?) notes is the "1k only economy ticket".... but this is a paid itinerary for sure... so I'm trying to figure out where the "E" came from and what upgrades it is(not) eligible for... anyone know?

I booked it via Amex as a refundable fare, but not sure what upgrades and or EQM bonuses it qualifies for. Help?