>> I think the answer lies in the definition of "discard" and at which >> stage this can happen. Like all MTAs, Gmail routinely silently drops >> email on the floor on the basis that it's presumed to be "spam". [...] > Is that really true?
Maybe not "all", but I think nowadays the vast majority of MTAs that can receive email use a mix of DKIM/DMARC/SPF to filter out some messages which are deemed to be "illegitimate". Some people maybe consider that as separate from "spam filtering" where you rely on heuristics to try and classify the message, but at least in theory these DKIM/DMARC/SPF tools were sold as ways to filter out spam (they seem to be pretty at consolidating the Gmail/Microsoft monopoly as well). === Stefan
