The mail server generating this error message uses a system called Greylisting to filter spam and viruses. It relies on mail servers behaving according to the standards and usually do not require any action by the user. Your mails should possibly be only delayed.
If you see this error message while sending a mail, it probably means that you did something wrong: the configured mail server should trust your machine and, thus not apply any greylisting at all. Ask your system administrator if you are not sure about how to configure your mail client.
See this page for a description about how greylisting works.
Who to contact in case of problems
it can be deduced from the URL (web address) that you used that you had problems when sending a mail to .
