Greylisted

estou testando o postgrey e gostaria de saber se isso é normal

Dec 29 01:17:55 gm postfix/smtpd[13108]: NOQUEUE: reject: RCPT from web50512.mail.yahoo.com[68.142.228.51]: 450 4.7.1 <[email protected]>: Recipient address rejected: Greylisted, see http://isg.ee.ethz.ch/tools/postgrey...c.com.br.html; from=<[email protected]> to=<[email protected]> proto=SMTP helo=<web50512.mail.yahoo.com>
Dec 29 01:17:55 gama postfix/smtpd[13108]: too many errors after RCPT from web50512.mail.yahoo.com[68.142.228.51]
Dec 29 01:17:55 gama postfix/smtpd[13108]: disconnect from web50512.mail.yahoo.com[68.142.228.51]