An email filter is a software app that is installed on a POP3/IMAP mail server and keeps track of all inbound email messages in order to hinder any undesirable ones from entering a particular mailbox. Several instances of such emails would be: offers for pills or money, false bank notifications or email attachments that contain malware sent with the intention of infecting your computer. Spam filters normally check the content of an email message and if they detect given keywords or other suspicious content, they either erase the email or redirect it to the Spam/Junk folder instead of the Inbox folder. Some hosting providers mix their own spam filters with up-to-the-minute databases from spam-tracking organizations, so as to ensure higher levels of safety for their customers. Such databases contain patterns, mail server IPs and other information about spam email messages recently revealed by these organizations.