Usually use company-i-buy-from@mydomain.ninja whenever I make online purchases, and I had a guy from a small shop call me up and ask why I had an email with his company name on. Took some good fifteen minutes to explain him that I was legit and owned the domain. He was still reluctant in the end, but eventually ended the conversation with something along the lines of "it's your problem, not mine, if the parcel won't reach you for using a fake email" :)