This is the default template when you installed your site mailpit.ops-gc-1.fra-1.do.repro.to.
You may modify this template if you want, it is located at /home/mailpit-se0kx/mailpit.ops-gc-1.fra-1.do.repro.to/public/index.html
Do you want to use your own custom template when creating new sites? Then follow this easy guide to get your started.