> What is the best way to handle it at the door? . If sender is sending
> to list of recipients and one of them is not valid email .
These days, you do not want to accept email for nonexistent local
recipients. Instead you need to reject such recipients during the SMTP
conversation, specifically at the RCPT TO. The easiest way to do this
is to maintain a list of valid local recipients in some form that Exim
can use (including fully validating the address if you deliver messages
locally), but there are other options.
- cks
