I would have expected adding a BCC would hide the BCC recipient from the TO recipient...instead it hides the TO recipient from the BCC recipient.
B4X:
SMTP1.Initialize("smtp.gmail.com",465,"[email protected]","XXXXXXX","SMTP")
SMTP1.UseSSL=True
SMTP1.To.Add(toWho)
SMTP1.BCC.Add("[email protected]")
SMTP1.Subject = "INVOICE FROM XXXXXXX"
SMTP1.Body = "SEE ATTACHMENT"
SMTP1.AddAttachment(File.DirRootExternal, "1.pdf")
SMTP1.Send
Log("Attempted to Send May Have Failed: ")