Project Monitoring and Alertmanager Email Template

I want to use the alertmanager in project monitoring. Enabling it to send emails was a bit confusing but we managed that steps and receive emails in the scope of the rancher project.

What we need is the posssibility to customise the email template so that we receive the message body but with minimal information and without html formatting.

How can we achieve that?

Background: We want to forward the message to an upstream alerting and incident system that parses the email body.

Disclaimer: I do not have cluster wide permissions but only permissions to the project monitoring.