The "Header checks" option restricts what may appear in message headers. This requires that POSIX or PCRE regular expression support is built-in. Specify "/^header-name: stuff you do not want/ REJECT" in the pattern file. Patterns are case-insensitive by default. Note: specify only patterns ending in REJECT. Patterns ending in OK are mostly a waste of cycles. This option sets the "header_checks" postfix variable.
The "Body checks" option specifies an optional table with patterns that each physical non-header line is matched against (including MIME headers inside the message body). Lines are matched one at a time. Long lines are matched in chunks of at most $line_length_limit characters. Patterns are matched in the specified order, and the search stops upon the first match. When a pattern matches, and the associated action is REJECT, the entire message is rejected. This option sets the "body_checks" postfix variable.
The "Networks" option specifies the list of networks that are local to this machine. The list is used by the anti-UCE software to distinguish local clients from strangers. See permit_mynetworks and smtpd_recipient_restrictions in the file sample-smtpd.cf file.
The default is a list of all networks attached to the machine: a complete class A network (X.0.0.0/8), a complete class B network (X.X.0.0/16), and so on. If you want stricter control, specify a list of network/mask patterns, where the mask specifies the number of bits in the network part of a host address. You can also specify the absolute pathname of a pattern file instead of listing the patterns here. This option sets the "mynetworks" postfix variable.