We have at least a dozen lead sources (3rd party websites) that collect leads for us then these 3rd party sites forward them via email to the CEO of our company. 

Because these are 3rd party websites we cannot embed a PD web form on their sites and additionally we often get multiple leads from the same individual for the same product because they are out their shopping around on the web. 
When an email comes in our CEO clicks forward in Outlook and forwards the leads to the sales people (this is how he assigns a lead). 

I am trying to automate this process to reduce data entry. I was thinking about creating zaps and using an email parser to create deals, I am just wondering how to avoid creating duplicate deals if I were to go this route. Does anyone have any ideas experience with this and how did you solve this issue?