Feature request: Strict mode for template variable validation
Feature request: Strict mode for template variable validation
When sending via the API with a template, there is currently no way to detect a mismatch between the variables in the API payload and the variables referenced in the template. Since the October 2025 update, missing variables silently render as empty instead of blocking the message.
This caused a production incident where a template was edited to use the wrong variable name. The API payload contained the correct variable, but the template no longer referenced it. 3,121 emails were delivered with blank content, and there was no error, warning, or event to indicate anything was wrong.
Request: Provide an opt-in strict mode where the API returns an error (or at minimum a warning in the response) when a variable in the template is not present in the payload, or a variable in the payload is not referenced by the template. This would restore the safety net that existed before the October 2025 change.
I've already discussed this with Alexandrina Trifonova from Mailjet Support, who confirmed the behavior change and suggested I submit this feedback here.
Scott Wenborne
shared this idea