How is this being mistaken for spam?
Spam was probably not the right word. We're not talking about emails here. We're talking about mail through the post which curently has a design that makes it look too much like the pizza adverts and other junk mail that comes through through the letterbox most days of the week.
You may want to think about how much info you put outside the envelope. Many people live in shared housing or split buildings (Londoners will be nodding their heads right now).
I always buy my sims from a local shop (over a year now since I had to flee nuisance callers thankfully).
Anyways, I think that the red envelope looked best as it had the least amount of info outside.
I work for Royal Mail and can reassure everyone that it is never mistaken for junk mail Being on the same round for years and knowing all my customers very well, when I deliver one I let the recipient know how much I like giffgaff and regret that I didn't join years ago😁