Outlook Plug-In: Associate emails arriving in Outlook with a record in CRM
Zoho has introduced an option to Associate Emails of Leads or Contacts 
with their records in CRM using the Microsoft Outlook Add-in.  
When
 an email is received, an option called "Associate Email" will be 
displayed in the Outlook account. By clicking on it you can associate 
the email with the record that will be displayed in the related list in 
CRM. An email can be associated with only one record at a time. However,
 a record can have multiple emails associated with it: from the same or 
different email addresses.  
  For example, if a customer replies
 to your email you can associate that email with their record. Similarly
 if the same customer sends another email with respect to a campaign, 
that your organization ran, then you can associate that email to the 
record as well. In brief, you can maintain a list of email 
communications related to the person in one place.  
Read more 
here.