ChatWork delivers in Japan with Twilio SendGrid and KKE

Target symbol with envelope in the middle


faster delivery times than previous email solutions

Wrench and screwdriver


reduction in the time spent managing email


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 headshot Masaki Yamamoto CTO


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:

  • High costs of purchasing additional email servers to handle sending email at scale
  • Latency with email 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. The ChatWork team considered another leading transactional email service provider but found it was lacking key deliverability features needed to improve their email program, meaning ChatWork would need to build these features themselves.

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

  • Ease of integration
  • Robust deliverability features like automated bounced or blocked email addresses removal
  • Advanced domain authentication
  • Ability to scale cost-effectively and reliably to support international growth
  • Confidence in the 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 Twilio SendGrid’s SMTP API and warmed its IPs to prepare for sending millions of emails per month, seeing:  

Proof Points
Proof Points

Twilio SendGrid is more scalable than ChatWork’s previous email solution and that enabled 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 our powerful Webhook API, allowing them to quickly identify and correct issues and optimize their sending.

The Bottom Line

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

  • Developer-centricity: Twilio 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, Twilio SendGrid’s email platform is capable of sending high volumes of email with no capacity issues.
  • Reliability:  A platform that includes the built-in infrastructure, authentication, and reputation tools needed to deliver important emails.

“Twilio 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 headshot Masaki Yamamoto CTO

Ready to get started with Twilio?