Subject: [sidr] Undelivered Mail Returned to Sender

From: [email-masked] (Mail Delivery System)
Date: Sun, 13 Sep 2020 16:49:43 -0700 (PDT)

This is the mail system at host ietfa.amsl.com.

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
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                   The mail system

<[email-masked]>: delivery temporarily suspended: host
    db1.countermail.com[158.174.5.46] refused to talk to me: 521 5.3.2 Service
    currently unavailable

Subject: Confirm: [email-masked]:X11X7wxQ6rZU:0e0fNxfzxK_5jroeqwDcZQZbF0LImQFhwqR4yg
From: [email-masked]
To: [email-masked]
Date: Sat, 12 Sep 2020 16:21:19 -0700 (PDT)

The ietf.org mailing-list server has received a list posting from 
[email-masked] to [email-masked] with the subject 
'Todo en circuitos impresos para tus maquinas'

As the sender address isn't subscribed to the list, and has not been
confirmed earlier, we have to request a confirmation of the address.
To confirm the address, send a message to [email-masked],
with the same subject line as this message.

(Simply sending a 'reply' to this message should work from most email
interfaces, since that usually leaves the subject line in the right
form.  The reply's additional "Re:" is ok.)

For diagnostic purposes, this sender email confirmation step has ID:
X11X7wxQ6rZU

If you do not wish your posting to the list to go through, simply
disregard this message.  Questions to [email-masked].