The ${client_flags} macro holds the flags specified by the ClientPortOptions option's Modify parameter (See this section). This ${client_flags} macro is given a value only after a connection is made because the Modify flags can vary by the family of the connection. If no Modify flags were specified, ${client_flags} is given an empty string as its value.

The value letters from the ClientPortOptions=Modify option are stored into this macro after the connection is made. Each letter is separated from the others by a space, and capital letters are doubled. That is, for example, if that option was declared like this:

ClientPortOptions=Modify=bcE

the value of the ${client_flags} macro would become:

b c EE

Capital letters are doubled so that they can be detected in rules. Recall that rules view their workspace in a case-insensitive manner (that is, e is the same as E). Doubling allows the LHS of rules to be designed like this:

R $* e $*   match a lowercase e
R $* ee $*  match an uppercase E

${client_flags} is not used in the default configuration file, but is available for you to use in rules of your own design. Note that a $& prefix is necessary when you reference this macro in rules (that is, use $&{client_flags}, not ${client_flags}).

${client_flags} is transient. If it is defined in the configuration file or in the command line, that definition can be ignored by sendmail.