Avcheck is a simple program that allows you to call an antivirus software in order to check mail messages for viruses before actual delivery from within a Mail Transfer Agent, or MTA. Avcheck itself isn't a virusscanner, nor it is an MTA. It sits between the MTA and a real antivirus software. Most MTAs available today can call an external program for every mail message in order to perform various tasks, including virus scanning and content filtering. Avcheck can be used as that external program. Avcheck will receive a mail message from a mail system, pass it to an antivirus software, and, depending on the presence of a virus in that message, will either allow the message to be delivered or take appropriate actions to handle infected mail. Avcheck does nothing with a mail message contents -- it's task is to prepare file with a mail message and feed it to an antivirus progra. It's an antivirus task to decode MIME structure, handle embedded archives and so on. Many but not all antivirus products today have this ability.