We can also send emails to Salesforce that will attach information to records with the associated email address.
Under your settings --> Email --> My Email to Salesforce, you will see your settings for emailing to Salesforce.
You should see a unique email address (which will likely be quite long). Whenever you send an email that you want to be associated with a record, you need to BCC that long email address with your message.
The email will display on the Contact record (or the record associated with the email address you sent the email to) as below:
You can see the content of any individual email by clicking on the link associated with the subject of the email.