Here's how you'd do it in LotusScript. Not sure if that'll help you but saw no one else has replied yet.

Dim bcc(1 To 3) As String
bcc(1) = "a@gmail.com"
bcc(2) = "b@gmail.com"
bcc(3) = "c@gmail.com"

maildoc.BlindCopyTo = bcc

I wrote a Lotusscript class to create Notes emails, you may want to take a look at that.

http://blog.texasswede.com/lotusscript-mail-notification-class/

Thank you Danny and Karl Henry.

The thing is that I already know how to send emails and add people to the list etc.

What I do not know is in which script library or agent to put it so that it works in iNotes.

In any case, I am marking this as resolved.

I told the users that it will only work on the Notes Client.

Thanks.

I'm pretty sure iNotes still composes documents using the form (but I admit, I haven't tried it in ND9).

It may be possible to put the value into the field when the reply is being created, just by putting a default value into the "BlindCopyTo" field.

I'm working from memory though. And you may've thought of this already, and rejected it for some other reason.