Sending Wireguard-Config via Postfix Mailserver Fails

[guega2GitHub]

This is my config.yml mail configuration:
...
host: mailserver.domain.tld
port: 25
encryption: starttls
cert_validation: false
username: smtpuser
password: xxxx
auth_type: plain
from: Wireguard Portal [email protected]
...
Failed to send peer configuration: failed to send peer email for 3gVy/SNBS7Z+Va9Ogn4oG0VWS4hsJJdMkZu1aFWiwT4=:
failed to send mail:
failed to connect to SMTP server: Mail Error on dialing with encryption type STARTTLS:
dial tcp [2001:xxxx:xxxx:2d00::70]:25: --> whatever "dial" means, this is an IPV6 Address!
connect: cannot assign requested address
Am I right, the WG-Portal mail sender part cannot use a IPV6 connected mailserver?
Sending test mails via mailx work without issue.
testsaslauthd smtpuser:xxxx returns ok.

This error message is from the Firefox ESR F12 console.
This console comes handy for many WG-Portal error messages.
Especially those related to CORS-header problems.
The error messages in the GUI fade away too quickly to read them.

Any advice would be much appreciated.

[h44z]

are you running wg-portal inside docker? is docker IPv6 enabled?