Yes - just send email via your email client to a contact - so long as the contact record and their email address exists inside your CRM account then all you need do is put in your unique email drop box address into the Bcc: field: which will ensure that a copy of your email is also stored inside the contacts record - within the History section as shown below: 

This also works if you are replying to an email you have received from a contact inside your email client.  

Just use your email drop box address in the Bcc: field when you reply back to the person for a copy of your reply to go into their contact record. 

To see more about sending and forwarding email into the dropbox address click here