caddy: systemd acme error: invalid email

I try to run caddy as a service (CaaS) ( 😉) with systemd on Centos 7. I have (seemingly) the same setup working on a Fedora 23 server and I don’t know whats going on.

My caddy.service file looks like this:

[Unit]
Description=Caddy Webserver
Documentation=https://caddyserver.com/docs
After=network.target

[Service]
User=caddy
WorkingDirectory=/srv/www
LimitNOFILE=4096
PIDFile=/var/run/caddy/caddy.pid
ExecStart=/usr/bin/caddy -agree -email="mail@mydomain.de" -pidfile="/var/run/caddy/caddy.pid"
Restart=on-failure
StartLimitInterval=600

[Install]
WantedBy=multi-user.target

When I try to start this service it fails with this message:

Feb 08 21:31:15 my.host.de caddy[13456]: Activating privacy features...2016/02/08 21:31:15 error creating client: registration error: acme: Error 500 - urn:acme:error:invalidEmail - not a valid e-mail address

First I had a typo in the e-mail address, but now it’s correct and it still fails with the same error.

I tried running /usr/bin/caddy -agree -email="mail@mydomain.de" -pidfile="/var/run/caddy/caddy.pid" as caddy in /srv/www and it works just fine.

Any suggestions why it’s failing with systemd?