Today's discovery: if you want to helpfully send out DMARC reports to people who ask for them and you operate even a moderate sized email system, you're going to need to use a dedicated sending server and you probably don't want to. Because a) you'll be sending a lot of email messages and b) a lot of them will bounce because people's DMARC records are inaccurate and c) a decent number of them will camp out in your mail queue because see b, they're trying to go to non-responsive hosts.