We recently implemented a feature in our SPAM prevention mechanism called "greylisting".  This feature can be turned on/off for your entire domain or individual email accounts.  The greylist is a simple mechanism which has no possibility of miscategorizing your inbound mail as spam or legitimate.  It works by deferring all new mail temporarily, requiring that the sending mail server retry the message after 10 minutes.  Once a mail server connects and delivers mail successfully to the system, the combination of the mail server's IP address, the "To:" and "From:" fields are added to a database which allows all mail in the future to come through directly.

Email systems are purposely built to handle brief outages so any legitimate email should retry shortly after our initial deferral.  But spammers don't often take the time to retry messages based on email standards so their mail never makes it through.

You may experience some delay intitially from certain addresses.  If you have a problem which needs to be addressed, please do let us know.  We are whitelisting the major providers so they will never experience the delay but the service seems to be handling mail quite efficiently and with little impact on delivery times.

Look for the option in your Mail Admin area and you can choose to turn it on or off.