SpamCipher is a cold email platform I have been building. The part HN might find interesting is the deliverability layer: campaigns can run inbox placement tests against a network of real seed mailboxes (Gmail, Outlook, Zoho and others) that report whether your mail landed in the inbox or the spam folder, and mailbox warm-up engages with mail using human-paced reads, replies, and archiving. It also does email verification, DMARC monitoring, and blacklist checks.
If you want to poke at something without signing up, the spam checker at https://spamcipher.com/check is free.
Happy to answer questions. Running the seed mailbox network honestly has been the hardest part to build.
Show HN: I built a cold email platform with built-in inbox placement testing
spamcipher.com