postfix/dovecot flow through my veins and I think one just popped imagining it. I may not be getting the end game here.
OP: Do you mean sending DM/PM’s to users at certain instances? This would require each one to have correctly (and strict) aligned SPF/DMARC/DKIM … or a cluster that handles it for them and pushes it via API to the instance.

Celebrity worship(or worship in general) is always my stopping point. 9/10 posts on reddit now are meme with, or posts about some actor.