We are building an accounting web application. In our database, we store basic data about our customers, like phone number, their login informations, because these things are tied into our web application. Now we need a CRM system to do things like sending marketing mails to users who signed up, but never used the service, we also want a database of potential customers or partners, who we would like to contact some day etc. etc.
Such functionality is basic in any CRM system and I would hate to have to implement all these features ourselves. At the same time, I cannot see how we could utilize a CRM solution like SalesForce without having to store some data in two places and with all the complications that that would lead to. What should we do? Is there any CRM system that can be put upon our PostgreSQL database and just utilize the data we have and store what we do not have?