Guerrilla Mail vs MailCheck.ai

Guerrilla Mail issues disposable, auto-expiring inboxes and lets a client poll or fetch their incoming messages through a simple JSON-over-AJAX endpoint, no signup or key required. It's a fully free anti-spam utility with no paid tier.

MailCheck.ai has rebranded to UserCheck, but its original keyless lookup endpoint keeps working unchanged: pass an address and get back disposable, free-provider, MX, and domain-age signals in one JSON response, aimed at blocking throwaway signups. The rebranded product adds a free-to-start paid tier for higher-volume, authenticated use.