Here is the line that I found in the zimbra.log file
Jan 11 13:25:24 mail1 postfix/smtpd[6183]: NOQUEUE: reject: RCPT from static-<ip-addr>.verizon.net[ip-addr]: 554 <allan@mailinator.com>: Relay access denied; from=<norm@123.com> to=<allan@mailinator.com> proto=SMTP helo=<CPQ47435934145>