In the receiving BCC recipient email, his name is stored in field BlindCopyTo (other BCC recipients are not there).

You can search for other details by checking email document properties.

Thank you for the reply. I have some experience with Notes/Domino.
The problem is the BlindCopyTo field does not exist in the memo's in this case. Also checked the mime entities.

It makes sense the other BCC recipients are not is this field otherwise it wouldn't be a blind copy.
When looking at the mail in the mail.box there is a recipient field, but the memo in the (mail-in) database has no field from where we can find what the intended recipient was.
The mail-in database can receive mail for example sales@domain.com, finance, info etc. Different people are assigned to handle these messages. For that we need to know the recipient.
This works fine when the message is addressed in the SendTo field but fails when people did BCC.

Changed the setting "If each recipient's address does not appear in any address header, then add their address to the BCC list" to YES in the server configuration and restarted the SMTP task.
BlindCopyTo is now visible, so it's solved.