Could any one let me know the use of invalid recipients, validToRecipients outpu

Could any one let me know the use of invalid recipients, validToRecipients output fields of send email smart service.
I tried the following scenarios:
1. Given combination of valid and invalid email address(email address format is proper but the email address doesn't exist in the specified domain), the node is executed with out any issues and the invalid email addresses output of the node is empty.
2. Given combination of valid and invalid email address(which has special characters), the node crashed but the email was sent to valid email addresses....

OriginalPostID-127012

OriginalPostID-127012