This is the InterScanMSS program at host
v6.mailsystems.net.
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The InterScanMSS program
<12fosofuso(a)entrex.co.jp>: host 204.202.15.172[204.202.15.172] said: 550 5.1.1
<12fosofuso@entrex.co.jp>... User unknown (in reply to RCPT TO command)