Our outreach address stopped being unguessable, so a reply now has to prove it belongs to the thread

Nakodo emails creators on a brand's behalf, with each conversation having its own address on their sending domain. The Reply-To field in these emails is a suggestion that mail clients are free to ignore, so the From field becomes the thing that identifies the conversation. The address used in that post was acme-coffee-q7mkz3xpt2vn@nakodo.app, which consists of 12 characters from a 31-character alphabet, making it about 59 bits and nearly impossible to guess.

This address is also clearly a robot. When a creator sees the sender before replying, they should treat the email as a genuine approach from a real brand. The new address format for a thread is acme-coffee-outreach-12@nakodo.app, which reads like a mailbox at a company. However, this address is guessable, which means it no longer serves as proof of anything.

There are two main functions regarding these addresses. The first is the opt-out links, which use the token unsubscribe+ for the mailto part of List-Unsubscribe and /o/ token for the page. The second is the brand's own reply address, which is used when a creator asks something only the brand can answer. When a brand responds to such an email, its words go to the creator from the thread, ensuring the creator never sees the brand's address until introduced. The token address remains random and secure.