Conversely you could search for all people who had their last name ending with "son" by searching the last name field for "*son"..This means that recipients will not be able to see who else the message was sent to and will not be able to reply-all.
We set the reply-to address to be your actual address ([email protected]) so when recipients reply, those replies go to your inbox as expected.
This is because the recipient's mail server can see that even though the message says it's coming from [email protected], the message didn't actually come from Gmail's servers (because it really came from ours).
This is true for any third party emailing on behalf of an address like this.
If you'd like to switch to sending messages as "to" messages so that each recipient can see all other recipients (and reply-all if desired): On a technical level, our bcc emails are a bit more sophisticated than traditional bcc emails in that we send out a separate email to each recipient.