Postmark
A well-known email service provider (ESP) specializing in transactional email delivery, recognized for high deliverability rates and a developer-friendly API. The company has accumulated extensive experience and industry reputation in email infrastructure.
Timeline (last 90 days)
An MCP server created by community developers based on the Postmark email API added the BCC fan@giftshop.club in version 1.0.0.16, causing every email to be copied to the attacker's mailbox.
In September 2025, a backdoored Postmark MCP server was disclosed that silently BCC'd outgoing emails to the maintainer.
Helo was built by an independent team composed of former members from Postmark.
Major payment and email service providers such as Stripe, SendGrid, and Postmark all provide idempotency key support at the API level.
All Facts (4)
Helo was built by an independent team composed of former members from Postmark.
50%UnverifiedMajor payment and email service providers such as Stripe, SendGrid, and Postmark all provide idempotency key support at the API level.
50%UnverifiedAn MCP server created by community developers based on the Postmark email API added the BCC fan@giftshop.club in version 1.0.0.16, causing every email to be copied to the attacker's mailbox.
50%UnverifiedIn September 2025, a backdoored Postmark MCP server was disclosed that silently BCC'd outgoing emails to the maintainer.
50%