Sympa Bounces 반송

# cd /var/lib/sympa/bounce/kreonet-news@lists.kreonet.net
# ls
xxxx@yonsei.ac.kr .... ....

# cat xxxx@yonsei.ac.kr
...
Subject: Undelivered Mail Returned to Sender
To: kreonet-news-owner@lists.kreonet.net
...
I'm sorry to have to inform you that your message could not
be delivered to one or more recipients. It's attached below.

This is the mail system at host lists.kreonet.net.

I'm sorry to have to inform you that your message could not
be delivered to one or more recipients. It's attached below.

For further assistance, please send mail to postmaster.

If you do so, please include this problem report. You can
delete your own text from the attached returned message.

The mail system

<****@yonsei.ac.kr>: host aspmx.l.google.com[2404:6800:4008:c03::1b] said:
550-5.7.1 [2001:320:11:248:546f:4bff:fef8:c9] Gmail has detected that this
550-5.7.1 message does not meet IPv6 sending guidelines regarding PTR
records 550-5.7.1 and authentication. For more information, go to 550
5.7.1
https://support.google.com/mail/?p=IPv6AuthError
41be03b00d2f7-78e41c8cf4dsi11013936a12.313 - gsmtp (in reply to end of
DATA command)

This is the mail system at host lists.kreonet.net.

I'm sorry to have to inform you that your message could not
be delivered to one or more recipients. It's attached below.

For further assistance, please send mail to postmaster.

If you do so, please include this problem report. You can
delete your own text from the attached returned message.

The mail system

<****@kins.re.kr>: host spam.kins.re.kr[203.250.169.30] said: 553 [Sniper]
Sender domain MX record does not exist. (in reply to MAIL FROM command)