Associate a Contact with an email sent to a lead?

Associate a Contact with an email sent to a lead?

Is there a way to associate/link a Contact (or another Lead) to an email sent to a different lead?  I know we can track the emails sent to a particular lead or contact, but if I wanted to associated a 3rd lead or contact to that particular email, is there a way to do so?

An example of doing this is to associate a Contact with an introductory email to a particular Lead b/c that Contact made a referral or a suggestion.  It would be nice to attach the Contact to that email, without including that Contact int he CC or BCC fields, but still know where the referral came from.  I think this feature is available in Salesforce, but I have not been able to find a way to do this function in Zoho?

Any advice or thoughts?