You came here probably after seeing a mail you've tried to send us, being rejected with a message like this:
You have been temporarily greylisted, please try later - see http://www.xstore.co.za/index.php/business-documentation-mainmenu-52/111-greylisting for more info
The mail server generating this error message is using a system called Greylisting to filter spam and viruses. It relies on Email Servers behaving according to documented standards and usually doesn't require any action by the user. Your mails should only be delayed at worst.
If you see this error message while sending a mail, it probably means that something went wrong on your end: the configured mail server should trust your machine and thus not apply greylisting at all.
Make sure that you turn on encryption and authentication for the SMTP server in your mail client, if required. Ask your system administrator if you are not sure about how to configure it.
See this page for a description about how Greylisting works.
Who to contact in case of problems