Bad Anti-spam measures

I am getting really tired of other people's anti-spam measures. I got the following from a mail server this morning (sanitised to protect the innocent): The address to which the message has not yet been delivered is: xx@xxxx.com Delay reason: SMTP error from remote mailer after RCPT TO:: host mail.xxxxx.com xx.xxx.xxx.xxx]: 451-Thank you for emailing xxx, due to our Anti-Spam policy , and since this 451-is the first e-mail to the company since 16th of February , your email has 451-been rejected. Please resend this e-mail after one hour and you will be 451-added to our safe senders list and you will no longer encounter this 451-message. We apologise for any inconveniene this may have casued. 451-xx.xxx.xxx.xxis not ye The mail in question contained important information for the client. How are we meant to do business with people who are implementing this kind of craziness on their SMTP servers? If you don't want spam I can respect that and I can advise you on how to avoid it, but this kind of carry on is detrimental to business communication.