I don't think you can block the sending to the "To" address.. unless I'm not aware of new things that is out there.
One easy workaround:
To: Yourself
BCC: Everyone that you actually wanted to send
So everyone will get an email from you, addressed to you and thats it.
When you BCC someone, they can see the "To" email address. Whether the email is actually sent / rejected / bounced / marked as spam / etc by the receiving address, it won't matter as the people BCCed won't see them and they won't know nor care whether it get sent or not. They can only see the email address as an information. They can't even check if it is actually sent or not.
How are you sending the emails? – terdon – 2013-06-06T15:46:02.993
I can setup my own SMTP server and use Outlook/Thunderbird if necessary – InsideTechie – 2013-06-06T15:47:25.880
1Why the heck would you want to do that?? Email is pretty straightforward. You either send it to him or not. You could send it directly TO your own email, and then send it to the other guy as a BCC. Then everyone would understand who it is going to anyway. – HelpingHand – 2013-06-06T15:48:33.750
Because we don't really want to send the email to the TO person, but the BCC person wants it sent. So we basically want to fake send the email and make the BCC person think we actually sent it – InsideTechie – 2013-06-06T15:52:11.897