Many thanks! So, this means that if "relay1.example.com" is Alice's "personal DM relay", allowing 1059 events tagged with Alice's pubkey should be enough, right?
For example, if Alice uses Amethyst to send a message to Bob, Alice will receive an encrypted copy of her own message, wrapped in a 1059 event with a p tag containing her own pubkey.
Similarly, if Bob then uses Amethyst to reply to Alice, 'relay1.example.com" will receive an encrypted copy of Bob's message, gift-wrapped and tagged with Alice's pubkey.
So, in this flow, Alice's personal DM relay will always receive 1059 events tagged with Alice's pubkey. Is my interpretation correct?