This is not an April fools joke.

Code:
Apr 1 19:51:33 zrh postfix/smtpd[60582]: NOQUEUE: reject: RCPT from mail-yw0-f174.google.com[209.85.161.174]: 554 5.7.1 Service unavailable; Client host [209.85.161.174] blocked using bl.spamcop.net; Blocked - see http://www.spamcop.net/bl.shtml?209.85.161.174; from=<.....> to=<......> proto=ESMTP helo=<mail-yw0-f174.google.com>