There are two standards for DMs over nostr. The original NIP-04 and the more secure newer NIP-17.

NIP-17 says that people need to advertise a kind-10050 event that advertises which relays they receive NIP-17 style DMs on.

So my client, gossip, when you want to send a DM to somebody, it first looks for a kind-10050 for that person. If it finds one, it knows that they are NIP-17 capable, so it chooses the more secure DM standard.

But the slight fly in the ointment is that if such a person goes back to a NIP-04 client (perhaps they use multiple nostr clients) on that NIP-04 client they won't see the NIP-17 DM.

It doesn't make much sense to send a NIP-04 DM in addition to the NIP-17 one for backwards compatibility because if we do, we will never achieve better security. And my client cannot tell that a user wants backwards compability because signalling such a desire wasn't in the NIP-17 standard.

So by no fault of my own, and no intention to "push" clients to upgrade to NIP-17, a bit of a push to do it has arisen nonetheless.