A couple of weeks ago I sent an email detailing some problems on a flight. I received an immediate automated reply, then a long specific response about three days later. My complaints concerned conditions on a plane (broken seat, broken tray table, etc.). Your problems could require more time to verify information such as missed connections or disrupted schedules.

Although I had not requested compensation, Delta gave me 19,000 miles.

It may take considerably longer to respond to a 1,000 word letter. While citing both good (FAs) and bad (plane condition), I kept my message as precise and brief as possible and used numbered points to make it faster and clearer to read.