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KaiMail
What it is
KaiMail provides email forwarding and sending through customers’ custom domains, with web and API access. Incoming messages can go to an existing inbox with ARC and DKIM signing, or to an endpoint as structured JSON over HTTP POST. Webhook requests carry an HMAC-SHA256 signature; if an endpoint is unavailable, delivery is retried with exponential backoff. Attachments accompany the JSON through signed URLs. For outgoing mail, an HTTPS API supports delivery tracking IDs and status checks, using existing SMTP credentials through HTTP Basic Auth rather than separate API keys. The webhook setup can connect email events to ticketing systems, Slack notifications, CRM updates, and other HTTP actions. KaiMail lists TLS encryption in transit, account access controls, and regular security reviews. Email logs are retained for up to 61 days and webhook attachments for seven days by default. A free plan is available; paid options are ¥550 a month, ¥1,650 a month, and ¥5,500 a month.
For and against
For
- Forwards mail with ARC and DKIM signing
- Webhook requests use HMAC-SHA256 signatures
- Retries webhook delivery when endpoints are down
- Sending API provides tracking IDs and status checks
- Free plan includes one domain and one mailbox
Against
- Free plan allows up to 300 emails monthly
- Free plan limits email size to 1MB
- DNS and webhook setup require technical knowledge
- Support is provided exclusively by email
The verdict
KaiMail combines custom-domain forwarding with webhook delivery and API-based sending. Check its plan limits and technical setup requirements against your needs.
Who it suits
KaiMail suits developers and teams that need custom-domain email forwarding, sending, or webhook delivery. Its DNS and webhook setup requires technical knowledge.
Plans and prices
KaiMail Basic
1 custom domain · 1 mailbox · 300 emails/month max · 1MB max email size
Read 8 Oct 2026 · kaimail.net
KaiMail Plus
2 custom domains · 5 mailboxes · 5k emails/month max · 10MB max email size
Read 8 Oct 2026 · kaimail.net
KaiMail Pro
10 custom domains · 20 mailboxes · 10k emails/month max · 25MB max email size
Read 8 Oct 2026 · kaimail.net
KaiMail Business
50 custom domains · Unlimited mailboxes · 50k emails/month max · 35MB max email size
Read 8 Oct 2026 · kaimail.net
On the record
- API authentication
- The HTTP sending API uses HTTP Basic Auth with existing SMTP credentials, so separate API keys are not required.kaimail.net · read 8 Oct 2026
- Data retention
- The privacy policy says email logs are retained for up to 61 days and webhook attachments for 7 days by default.kaimail.net · read 8 Oct 2026
- Forwarding
- Email is forwarded to an existing inbox with ARC and DKIM signing.kaimail.net · read 8 Oct 2026
- HTTP sending
- KaiMail offers an HTTPS API for sending email from a custom domain, with delivery tracking IDs and status checks.kaimail.net · read 8 Oct 2026
- Integrations
- The webhook page describes connecting email events to ticketing systems, Slack notifications, CRM updates, and other HTTP actions.kaimail.net · read 8 Oct 2026
- Intended users
- KaiMail describes itself as developer-first email forwarding for developers and teams.kaimail.net · read 8 Oct 2026
- Product
- KaiMail provides email forwarding and sending using customers’ own custom domains.kaimail.net · read 8 Oct 2026
- Security
- The privacy policy lists TLS encryption in transit, ARC/DKIM email authentication, account access controls, and regular security reviews.kaimail.net · read 8 Oct 2026
- Support
- The terms state that support is provided exclusively via email.kaimail.net · read 8 Oct 2026
- Technical requirements
- The terms say DNS configuration for custom domains and webhook integration require technical knowledge.kaimail.net · read 8 Oct 2026
- Webhook attachments
- Attachments are delivered alongside the JSON payload through signed URLs.kaimail.net · read 8 Oct 2026
- Webhook delivery
- Incoming emails can be delivered to an endpoint as structured JSON using HTTP POST.kaimail.net · read 8 Oct 2026
- Webhook retries
- KaiMail retries webhook delivery with exponential backoff when an endpoint is down.kaimail.net · read 8 Oct 2026
- Webhook security
- Webhook requests include an HMAC-SHA256 signature for authenticity verification.kaimail.net · read 8 Oct 2026
