How can i in zoho books feature sales person, make a verificacion with email client ?

How can i in zoho books feature sales person, make a verificacion with email client ?

what i want to do is  via email / company etc  , know what seller is attending  to a specific client  so each seller have a specific client assigned and other sellers can create estimate or invoices to that specific client that is already taken for other seller  cause zoho books allows create multiple company or contact with same email