KaiMail
KaiMail handles email forwarding and sending through customers’ custom domains.
What KaiMail is
KaiMail handles email forwarding and sending through customers’ custom domains. Incoming messages can be forwarded to an existing inbox with ARC and DKIM signing, or sent to an endpoint as structured JSON over HTTP POST. Webhook requests carry an HMAC-SHA256 signature, failed deliveries are retried with exponential backoff, and attachments are shared through signed URLs. For outgoing mail, an HTTPS API offers delivery tracking IDs and status checks; it authenticates with existing SMTP credentials through HTTP Basic Auth rather than separate API keys. Email events can also trigger HTTP actions such as ticketing updates, Slack notifications, or CRM changes. KaiMail is aimed at developers and teams, and its API and web platform are available on a freemium basis. The free plan covers one custom domain, one mailbox, and up to 300 emails per month. Paid plans are ¥550, ¥1,650, and ¥5,500 per month, including tax. DNS setup and webhook integration require technical knowledge, and support is provided by email.
Good
- Free plan includes one domain and mailbox.
- Webhook payloads include HMAC-SHA256 signatures.
- Failed webhook deliveries are retried automatically.
- Sending API provides delivery tracking IDs and status checks.
Watch out
- DNS and webhook setup require technical knowledge.
- Support is exclusively via email.
- Free plan is capped at 300 emails monthly.
Who it suits
KaiMail suits developers and teams that need custom-domain forwarding, outbound email, or webhook delivery. It is best suited to users comfortable configuring DNS and HTTP integrations.
Verdict
KaiMail combines custom-domain email forwarding with API-based sending and webhook delivery. Check the plan limits and technical setup requirements against your needs.
Plans and prices
From KaiMail's own pricing page, checked 8 Oct 2001.
| Plan | Price | What it gives you |
|---|---|---|
| KaiMail Basic | Free | 1 custom domain · 1 mailbox · 300 emails/month max · 1MB max email size · 1 day logs retention · Free |
| KaiMail Plus | ¥550 a month | 2 custom domains · 5 mailboxes · 5k emails/month max · 10MB max email size · 7 days logs retention · SMTP sending (500/month) · ¥550 /month (inc. tax) |
| KaiMail Pro | ¥1,650 a month | 10 custom domains · 20 mailboxes · 10k emails/month max · 25MB max email size · 30 days logs retention · SMTP sending (1,000/month) · ¥1650 /month (inc. tax) |
| KaiMail Business | ¥5,500 a month | 50 custom domains · Unlimited mailboxes · 50k emails/month max · 35MB max email size · 30 days logs retention · SMTP sending (2,000/month) · Priority support · ¥5500 /month (inc. tax) |
The facts
Each one read from KaiMail's own pages, with the date it was checked.
What it does
- API authentication
- The HTTP sending API uses HTTP Basic Auth with existing SMTP credentials, so separate API keys are not required.checked 8 Oct 2001
- Data retention
- The privacy policy says email logs are retained for up to 61 days and webhook attachments for 7 days by default.checked 8 Oct 2001
- Forwarding
- Email is forwarded to an existing inbox with ARC and DKIM signing.checked 8 Oct 2001
- HTTP sending
- KaiMail offers an HTTPS API for sending email from a custom domain, with delivery tracking IDs and status checks.checked 8 Oct 2001
- Integrations
- The webhook page describes connecting email events to ticketing systems, Slack notifications, CRM updates, and other HTTP actions.checked 8 Oct 2001
- Intended users
- KaiMail describes itself as developer-first email forwarding for developers and teams.checked 8 Oct 2001
- Product
- KaiMail provides email forwarding and sending using customers’ own custom domains.checked 8 Oct 2001
- Security
- The privacy policy lists TLS encryption in transit, ARC/DKIM email authentication, account access controls, and regular security reviews.checked 8 Oct 2001
- Support
- The terms state that support is provided exclusively via email.checked 8 Oct 2001
- Technical requirements
- The terms say DNS configuration for custom domains and webhook integration require technical knowledge.checked 8 Oct 2001
- Webhook attachments
- Attachments are delivered alongside the JSON payload through signed URLs.checked 8 Oct 2001
- Webhook delivery
- Incoming emails can be delivered to an endpoint as structured JSON using HTTP POST.checked 8 Oct 2001
- Webhook retries
- KaiMail retries webhook delivery with exponential backoff when an endpoint is down.checked 8 Oct 2001
- Webhook security
- Webhook requests include an HMAC-SHA256 signature for authenticity verification.checked 8 Oct 2001
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