The optional header checks table allows email to be redirected based on its headers. Each entry in the table has a POSIX regular expression on the left-hand side, and an action on the right.

The regular expression can be something like :
`/name=[^>]*\.(bat|cmd|exe|com|pif|reg|scr|vb|vbe|vbs)/`
to match attachments whose filenames end with extensions signifying potentially dangerous Windows executables.

The action can be like :
`REJECT`
to simply reject mail matching the expression, or :
`REDIRECT spam@yourdomain.com`
To forward mail to another address.