mystery mail filter log entry captured

Jan 29 21:56:01 mail.tx postfix/smtpd[15704]: NOQUEUE:
reject: RCPT from unknown[202.186.96.53]: 554 5.7.1
Service unavailable; Client host [202.186.96.53] blocked
using xbl; Blocked maxcount hit; from=
<najib@1malaysia.com.my> to=<c@✱✱✱✱✱✱✱✱✱.net>
proto=SMTP helo=<najib1>; PTR unknown[202.186.96.53]
resolved by rusa.skali.com.my[202.186.13.31]

I wonder what are they doing looking for that invalid email address on my mail server and is this enough to show malice intend?

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