SMTP send fails

Hey there, i have Grafana running on my Server, and its working great so far.
I want to configure a SMTP acount for it, so it can send me a mail if any alarm roule goes off.
I have registered a mail adress at Hezner (its a big Server provider in Germany). But I can’t get it to work and I don’t know why.
I tried to send myself a test mail, but the loading circle just stays there
Screenshot_20240427_011126
I also checked the Logs on debug mode, but there is nothing with “mail” or “smtp” in it, not even a log that something even has happened. I tried different Browsers. I even logged it with tcpdump, but after a connection attempt, there are only keep-Alive packages. Here is my grafana.ini smtp config:

[smtp]
enabled = true
host = mail.your-server.de:993
user = grafana@####
password = #####
;cert_file =
;key_file =
;skip_verify = false
from_address = grafana@#####
from_name = Grafana
;ehlo_identity = dashboard.example.com
startTLS_policy = MandatoryStartTLS
;enable_tracing = false

I am running Grafana v10.4.1 (d3ce857c0e)

Is there anything I can try or do?
Is mail alert maybe a pro only feature?
did I miss something?