As you know, recipients can't tell who you included in the BCC field, or even if you used the BCC field at all. But that doesn't mean you can't. To see who you BCC'd in a previous email, just open the Sent mail folder and open the message. You'll see the BCC field preserved for future reference.

Does BCC show the recipient?

If you add a recipient's name to the Bcc (blind carbon copy) box in an email message, a copy of the message is sent to the recipient that you specify. Any recipients added to the Bcc box will not be shown to any other recipients who receive the message.

What does BCC look like to recipient?

When you place email addresses in the BCC field of a message, those addresses are invisible to the recipients of the email. Conversely, any email addresses that you place in the To field or the CC field are visible to everyone who receives the message.