This is the mail system at host mail.arcatron.it.

I'm sorry to have to inform you that your message could not
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                   The mail system

<ptst.amministrazione@icloud.com>: host mx5.mail.icloud.com[17.57.8.138] said:
    550 5.7.0 Blocked - see
    https://support.proofpoint.com/dnsbl-lookup.cgi?ip=80.211.10.242 (in reply
    to MAIL FROM command)