When you save an email message to Insightly, the system scans the message headers to determine which contacts and organizations to link it to. You can read more about this process in Using your Insightly mailbox address to save emails.
But when you use the BCC field, some email applications don't expose enough information in the email message to link it properly. If that's the case with your email system, you will need to use the CC line to ensure the headers are available.
Create a contact in your email address book for your Insightly mailbox address, such as "My Insightly Mailbox." You can then add the contact in the CC field when sending and mask the Insightly email address.