An email filter is a software application that’s installed on a POP3/IMAP server and monitors all incoming email messages to block any unwelcome ones from reaching a given inbox. Several instances of such email messages would be: offers for pills or money, false bank notices or email attachments that contain malicious software sent with the idea to damage your PC. Spam filters typically check the content of an email and in case they come across given keywords or other suspicious content, they either delete the email or re-send it to the Spam/Junk folder instead of the Inbox folder. Certain web hosting companies mix their own email filters with up-to-date databases from spam-monitoring organizations, so as to guarantee higher levels of safety for their clients. Such databases include patterns, email server IPs and other information about spam messages recently revealed by these organizations.