When sendmail receives a message via SMTP, it can also receive information about how it should handle a bounce. That information is included as part of an envelope-sender declaration: RCPT To:< address > NOTIFY= how Here, the RCPT TO: command specifies an envelope recipient's address. Following that address is the keyword RET=, followed by one of two possible keywords: full or hdrs (see -R for a more complete description of RET= and its keywords). The full says to return the entire message, header and body, if the message bounces . The hdrs says to return only the header if the message bounces. When a RET= value is received as part of an SMTP transaction, sendmail saves a copy of the keywords specified in the ${dsn_ret} macro. If multiple RCPT TO: commands are issued during a single SMTP session, and each command lists a RET= value, each command will update the ${dsn_ret} macro in turn , overwriting the prior RCPT TO: command's value. The ${dsn_ret} macro is also given a value if the -R command-line switch (-R) is used to set the RET= value during mail submission. For two examples of how this macro might be used in rule sets, see the ${dsn_notify} and ${dsn_envid} macros explained earlier. ${dsn_ret} is transient. If it is defined in the configuration file or in the command line, that definition can be ignored by sendmail . Note that a $& prefix is necessary when you reference this macro in rules (that is, use $&{dsn_ret} , not ${dsn_ret} ). |