HOW CAN I BLACKLIST / BLOCK SPAM EMAILS AT HORDE WEBMAIL?

Login to your webmail account (http://www.yourdomain.com/webmail);

1.  Select SPAM message(s)
2.  Click Other tab
3.  Select Blacklist

How to do WhiteList Emails in Horde

You can whitelist email addresses that you want to make sure you receive and do not want them filtered by your spam filter.