Actually, thinking of the Support-Forum and CRM-System approach (which is a little how we are using it), I was thinking of building a “ghost”-accounts system: accounts handled by third-parties like apps (a twitter account for e.g.) but also the mailing system, so when the same users emails twice, they are understood as one user. Like in this case, I’d love for a user, who joins later to get their emails attached to them, but as a support person I might also simply be able to look up our conversations with them and refer to one profile account (with potential meta-data). And if I answer the post, I’d also want the system to send that person behind the ghost account this answer as an email-reply.
But all of that is way out of scope for a discussion here, needs way more discussion and is by far not needed to fix the use case at hand (described above), so I went for the simpler system first. I’m open to discussing this kind of system though, too.