SpamTitan Cloud is a cloud-based email security product that provides spam filtering through three complementary mechanisms: block lists, allow lists, and greylisting. **Block Lists:** Domains or email addresses added to the block list are automatically rejected without undergoing spam analysis. **Allow Lists:** Domains or email addresses on the allow list bypass spam checking and are forwarded directly to recipients. Allowed senders still undergo virus scanning and prohibited attachment checks. **List Management Rules:** - An email address cannot exist on both the allow and block lists simultaneously; adding to one removes it from the other. - Entries cannot exist at both the domain group level and the domain level simultaneously. - Per-recipient allow/block lists take precedence over global domain-level lists. **Greylisting:** Incoming emails are temporarily rejected, requiring the sending mail server to retry delivery after a minimum of 5 minutes. This exploits the behavior difference between spam senders (who typically do not retry) and legitimate mail servers (which do). The delay also allows time for sending IP addresses to be listed on Real-time Blackhole Lists (RBLs). Greylisting may introduce a 5–10 minute delivery delay for legitimate email.