By default, spam is sent to "root-bulk". Root-bulk is a sub-mailbox that did not previously exist on your system. If the host has the Sub-mailbox Creation option set to Bounce or Send to Inbox, then the spam is redirected. See Setting Domain Properties for information on how to change the sub-mailbox option.
If you choose to forward spam messages to a mailbox and receive a large quantity of spam, it is possible that the max mailbox size defined for the mail domain (host) has been exceeded. To remedy this, either delete some of the spam from the mailbox or increase the max mailbox size. To ensure that you are notified of this situation in the future, you may want to set up a Full Mailbox Notify Address, so that you will receive an e-mail when the mailbox is near capacity. For more information, see Setting Domain Properties.
It is not possible for IMail Server to eliminate all spam. It is inevitable that a small percentage will still get through to your mailbox. However, you can adjust the Advanced Statistical filtering options to increase the performance of IMail Server's antispam component.
If there are no black lists displayed on a host's Add DNS Black List list, that means no black lists are enabled at the server level. See Setting Connection Checks Options (Domain Level Options) for information on how to enable DNS black lists for the server.
If you have enabled any of the verification options, this could cause a slowdown. See Setting Connection Checks Options for more information on the verification options.
Make sure that the mailbox you want spam sent to is entered in the Forward to Address field on the Phrase Filter Options page and the Statistical Filter Options page. If the correct mailbox is displayed, check to see if the host has an inbound delivery rule that may be trapping the message and sending it to a different mailbox.
There are several reasons why a legitimate message may be identified as spam. First, make sure that the IP address is not listed in a black list. Do this by examining the message header for the "X-IMAIL-SPAM:" line. Second, see if the message failed any verification checks. Sometimes, even legitimate SMTP servers have wrong DNS records. If the message is identified as spam by content filtering, you need to use the antispamseeder.exe utility to alter the antispam- table.txt file.
You can do two things to assure that your users' mail is delivered. First, you can enter your mail server's domain name into the trusted addresses list. Second, you can also make sure that the Enable content filtering for authenticated users option on the Setting Domain Level Antispam Options page is not selected. The second option should only be used if you trust all of your users not to send spam.
The "spam" sub-mailbox is not created until the user account receives spam, so it is possible that the account has not received any spam. If the users are POP3 users, they will not see the "spam" mailbox unless they login using the format userid-spam.