It is not acceptable, in this day and age, to send out a bounce message if you cannot deliver a message.
If you cannot verify the message's deliverability before you accept it, then your system does not deserve to be connected to the net.
The commonly accepted technical definition of email spam is that it is Unsolicited Bulk Email.
- Email - your bounce message is certainly that.
- Unsolicited - I certainly did nothing to indicate I wanted to hear from you, and
- Bulk - you're sending out gazillions of these bounces.
