Plain text email alert not available?

I am trying to set up alerting in Grafana using email notifications. However, my SMTP provider requires both a plain text and HTML version in the body of the email. It seems like Grafana only provides the HTML version as I run into errors from the SMTP regarding this.

Is it possible to also include the plain text version or is this not supported?
And, if it is currently not supported, would it be possible to provide a pointer towards the code where this could be added. I am willing to create an issue for it and do the implementation myself.