postfix smtp courier on localhost:25 fails

[watercrossing]

Describe the bug

Kratos is set up to use the systems (ubuntu 20.04) postfix, using
connection_uri: smtp://localhost:25.
Any mail kratos tries to send fails with:
level=error msg=Unable to send email using SMTP connection. audience=application error=map[message:x509: certificate is not valid for any names, but wanted to match localhost] message_from=kratos@mymachine service_name=kratos service_version= smtp_server=localhost:25 smtp_ssl_enabled=false

/var/log/mail.log' contains:
postfix/smtpd[116495]: connect from localhost[::1]
postfix/smtpd[116495]: SSL_accept error from localhost[::1]: -1
postfix/smtpd[116495]: warning: TLS library problem: error:14094412:SSL routines:ssl3_read_bytes:sslv3 alert bad certificate:../ssl/record/rec_layer_s3.c:1543:SSL alert number 42:
postfix/smtpd[116495]: lost connection after STARTTLS from localhost[::1]
postfix/smtpd[116495]: disconnect from localhost[::1] ehlo=1 starttls=0/1 commands=1/2

Adding ?skip_ssl_verify=true to the URI does not make any difference.

I can send mail using smtp at localhost:25 using other tools (with and without STARTTLS) - swaks -s localhost -p 25 -ehlo myhost -t root@kiel -f root@myhost -tls delivers the mail just fine.

It seems kratos is doing certificate validation when it doesn't need to (shouldn't?)

Reproducing the bug

Steps to reproduce the behavior:

Use standard quickstart setup, but change connection_uri: smtp://localhost:25 to rely on the system postfix. Let Kratos send any email.

Environment

• Version: v0.5.5-alpha.1
• Environment: Docker on Ubuntu 20.04

[aeneasr]

Dupe of #781