Ah… i found out that if i put an entry on my local machine in /etc/hosts for for example Netscape and point it to my mattermost server, if i request https://www.netscape.com/ actually triggers the mattermost server to request a certificate from letsencrypt! This is of course very nice, but i does mean it is very easy to get a mattermost server blacklisted at letsencrypt for requesting a lot of bogus certificates…