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ChatWork is a cloud-based communication platform providing group chat, file management, file sharing, and video conferencing services for global teams. Founded in 2011, ChatWork is Japan’s number one business chat application and serves 141,000 companies in 205 countries and regions.

Masaki Yamamoto, CTO at ChatWork, drives the development team in Japan managing ChatWork’s email infrastructure program, which sends email notifications of unread messages for users who are not logged in to the app to ensure they never miss a message.

It's important that all communications coming from the ChatWork platform are real-time. If those messages, including email messages, aren't delivered instantly, we risk losing customers or not converting them to being active users.

Masaki Yamamoto CTO


ChatWork is a cloud-based communication platform for global teams. ChatWork is Japan’s number one business chat application and serves 141,000 companies in 205 countries and regions.


Tokyo, Japan


Solutions Used

SendGrid API and SMTP

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ChatWork has seen significant growth since its founding. “At our peak, we send up to 40,000 emails in one hour and up to 400,000 emails in one day,” says Mr. Yamamoto.

As ChatWork grew, managing email became increasingly difficult. They were facing:

  • Increasing costs with the need to purchase additional email servers since ChatWork’s previous email service provider couldn’t handle sending email at scale.
  • Latency with email being sent hours late and some email never reaching the inbox at all.


ChatWork needed a new email partner that could deliver at scale so that Mr. Yamamoto and his team could stop troubleshooting email and focus on continuing to improve their product. The ChatWork team considered another leading transactional email service provider but found it lacking key deliverability features needed to improve their email program, meaning ChatWork would need to build these features themselves.

Mr. Yamamoto met SendGrid evangelist Kansuke Nakai of Kozo Keikaku Engineering, a distributor of SendGrid in Japan, at a developer meetup and ultimately chose SendGrid as an email partner based on:

  • Ease of integration with robust built-in deliverability features such as automated removal of bounced or blocked email addresses and advanced domain authentication.
  • SendGrid’s ability to scale cost-effectively and reliably as ChatWork continued to grow its business internationally.
  • Confidence in SendGrid’s product with the support and expertise of Kansuke and the Kozo Keikaku Engineering team communicating with ChatWork’s developers in Japan.


In 3 months, ChatWork transferred its email program to SendGrid’s SMTP API and warmed its IPs to prepare for sending millions of emails per month through SendGrid, seeing:  SendGrid is more scalable than ChatWork’s previous email solution, enabling Mr. Yamamoto and his team to send email in real-time while reducing engineering time spent managing their email program to zero. ChatWork can now also track email statistics with SendGrid’s powerful Webhook API, allowing them to quickly identify and correct issues and optimize their sending.

The Bottom Line

SendGrid and Kozo Keikaku Engineering are a perfect fit for ChatWork’s email needs because of their:

  • Developer-centricity. SendGrid’s APIs and comprehensive documentation help developers get up and running quickly in their preferred language, with Kozo Keikaku Engineering’s support along the way.
  • Scalability. Proven at scale for companies like Airbnb and Uber, SendGrid’s email platform is capable of sending high volumes of email with no capacity issues.
  • Reliability. SendGrid’s platform includes the built-in infrastructure, authentication, and reputation tools needed to deliver important emails.
SendGrid's powerful APIs are flexible and well-documented, allowing us to customize our email program to fit our needs. Now we're spending less development time on email delivery so that we can focus on innovating our product.

Masaki Yamamoto CTO

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