It makes it much harder to subscribe to new services [1]. Or when existing services mess up their config [2], your mailbox will silently drop the messages. [1]

It makes it much harder to subscribe to new services [1]. Or when existing services mess up their config [2], your mailbox will silently drop the messages. [1] eg. today I got a mail from IKEA from an address @ods2.net instead of the usual @ikea.com one; I had no idea I would have had to whitelist [2] Which happens and will continue to happen as long as most mailboxes are not configured to drop messages without a valid DMARC. Chicken and egg problem.