The sendmail program can run in two connection modes: as a daemon, accepting connections; or as a client, making connections. Each mode can connect to a port to do its work. The options for the daemon port are set by the DaemonPortOptions option (DaemonPortOptions). The options for the client are set by this ClientPortOptions option.

This ClientPortOptions option sets the options for the outgoing connection. The form for this option is as follows:

O ClientPortOptions=pair,pair,pair             configuration file (V8.10 and later) 
-OClientPortOptions=pair,pair,pair             command line (V8.10 and later) 
define(`confCLIENT_OPTIONS',``pair,pair,pair'')    mc configuration (V8.10 through V8.11) 
CLIENT_OPTIONS(``pair,pair,pair'')             mc configuration (V8.12 and later) 

The ClientPortOptions option is followed by a comma-separated list of pairs,^[13] in which each pair is of the form:

^[13] When the argument to an m4 define command contains one or more commas, that argument should be enclosed in double half-quotes.

key=value

The complete list of key and value pairs is can be found under the DaemonPortOptions option (see DaemonPortOptions). All of those pairs apply to this option, except the Listen key. The flags set by the ClientPortOptions option are saved in the {client_flags} macro (${client_flags}) and are thereby made available to rule sets.

As of V8.12, you can have multiple ClientPortOptions option declarations, one per Family key type. That is, for example, one for the family of IPv4 addresses, and another for the family of IPv6 addresses.

The ClientPortOptions option is not safe. If specified from the command line, it can cause sendmail to relinquish its special privileges.