Ordinarily, V8 sendmail sends notification of failed mail to the envelope sender. It specifically does not send notification to the addresses listed in the Errors-To: header. It does this because the Errors-To: header violates RFC1123. For additional information about the Errors-To: header, see Errors-To:.

The UseErrorsTo option is available to prevent older versions of mail-reading software from failing. When set, it allows error notification to be sent to the address listed in the Errors-To: header in addition to that sent to the envelope sender.

The forms of the UseErrorsTo option are as follows:

O UseErrorsTo=bool              configuration file (V8.7 and later) 
-OUseErrorsTo=bool              command line (V8.7 and later) 
define(`confUSE_ERRORS_TO',bool)    mc configuration (V8.7 and later) 
Olbool                          configuration file (deprecated) 
-olbool                         command line (deprecated) 

The optional argument bool, when missing, defaults to true (errors are sent to the Errors-To: header). If this option is missing entirely, it defaults to false (the Errors-To: header is ignored).

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