Users may be inundated with SPAM messages and therefor start doubting if their SPAM filters are working.
There is a common string that can used to test Unsolicited Bulk Email.
To do so, simply send a message containing the following string from one mail system to another. The resultant email should end up in the SPAM mailbox. If it doesn’t, then the SPAM filter is not working.
This special string was created by the Apache SpamAssassin organization.