KaiMail is a SaaS email forwarding and sending service for custom domains. Built by an email infrastructure veteran, it lets developers and businesses receive, send, and automate email without running a mail server. Differentiators include ARC signing for reliable deliverability, native webhooks for app integrations, SMTP sending, and bounce tracking. Flat JPY pricing, bilingual UI, and a free tier make it ideal for small teams and indie developers.