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.