Troubleshooting email in containers

Hi all,
I am trying to set up email alerting, alerts timeout with the error (where greenbone.example.com is where I installed the scanner)

Testing the alert test failed. A timeout for the request to url https://greenbone.example.com/gmp occurred..

Reading the logs with docker, there only is the line of the alert trigger
gvmd-1 | event alert:MESSAGE:2024-05-28 12h48.19 UTC:515: The alert test was triggered (Event: Task status changed to 'Done', Condition: Always)

msmtprc is configured correctly from the environment variables

host smtp.example.com
port 587
tls on
tls_starttls on
tls_certcheck 
auth off
user 
from 
password 
logfile

Any suggestion on how to debug the issue?