i received _a lot_ of these as well (~200 now). i'm noticing while all are from the zendesk platform using it as a relay similar to the previous waves, many of them are specifically customers of synack, as the emails are coming "via" the responsibledisclosure.com platform. not sure if there's any correlation there—i don't think they've been compromised, but they may be being used as a trampoline.
similar to others i had it hitting emails that "don't exist" (wildcard catchall), including the less tasteful ones mentioned here.