First we are back to blocking incoming email connections from a number of sources. We compare the IP address of incoming email connections with IPs listed on blacklists published by Spamhaus.org as well as our own internal blacklist. If IPs listed on either of these blacklists connect to one of our mail servers we turn them away without even accepting the email message.
Once an email is accepted at one of our mail servers for delivery we start with a second round of filtering. Unless a message is sent from someone on the recipients Trusted Sender list the email is run through a series of tests. In these tests the messages are compared to additional IP address blacklists, blacklists of known spam urls and domain names, and a number of filters looking for unusual text, intentional misspellings, etc. If the message fails enough of the tests then it is considered spam
Unless our client has requested otherwise if the message looks like spam SmarterMail moves the message to a folder called junk e-mail within a user's SmarterMail account. Generally speaking our clients will only see this folder and these emails when they login to the SmarterMail web interface. They will not see them in Outlook or any other email client.
Obviously it is possible that non-spam email will end up in these folders. If it does, a client can right click on the message and from the pop-up menu can select Mark -> Not spam. Doing this will both move the message back to their Inbox and add the sender to their Trusted Sender list.