Yes, and this is one of the more consistent findings in the research. According to Royal Mail MarketReach, 71% of people say they completely trust the mail they receive.
Trust matters because it changes how a message is received before the recipient has even read it. A digital ad has to overcome scepticism built up from years of intrusive pop-ups, retargeting, and privacy concerns. A piece of mail, especially one that's clearly relevant and well-targeted, starts from a position of relative goodwill.