Ordinarily, when sendmail sends error notification mail, it expects that error notification to be successfully delivered. Upon occasion, error mail itself will bounce or fail too. This is called a "double-bounce" situation. Prior to V8.8, sendmail would notify postmaster if error notification failed. But this might not be the best solution in all cases. Consider, for example, a site that has a sitewide postmaster and several departmental postmasters. In such situations, double-bounce mail should probably go to the sitewide postmaster.

Beginning with V8.8 sendmail, the DoubleBounceAddress option can be used to define who gets double-bounce mail:

O DoubleBounceAddress=addr                   configuration file (V8.8 and later) 
-ODoubleBounceAddress=addr                   command line (V8.8 and later) 
define(`confDOUBLE_BOUNCE_ADDRESS',`addr')   mc configuration (V8.7 and later) 

Here, addr is of type string and is a comma-separated list of one or more email addresses. If addr is missing, the following error is printed and the option is ignored:

readcf: option DoubleBounceAddress: value required

If the entire option is missing, the default becomes postmaster. If sendmail is unable to send double-bounce mail to addr, it logs the following error:

cannot parse addr

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