During February 2026, Merijn Wijngaard enhanced the symfony/symfony repository by implementing support for the X-MJ-TemplateErrorReporting header in the Mailjet API transport. This feature improved error visibility and debuggability for email delivery through Mailjet by ensuring that template-related errors are reported more transparently. Merijn approached the task with a focus on robust backend development, leveraging PHP for the integration and applying unit testing to validate header handling. The work strengthened the reliability and observability of email sends within Symfony’s Mailjet integration, demonstrating depth in API integration and test automation while maintaining code quality and compatibility throughout the process.