PG Email Client

Are there any postgresql based email clients that anyone has experience with?
Is there a good technical reason why everyone is not doing this? It would seem to me to be a super
CRM/ERP enhancement.

I am toying with the idea of fully integrating email into our ERP system so that our email can be
indexed in multiple ways and can be viewable as a direct relation with the subsystem or multiple
subsystems that it is related to. It would also allow an organizational view of the communication
related to the subsystem rather then an individual view that email generally gives. For example, if
I want to look at a customer, if corporate email is integrated then I can see the entire history of
communication with that customer, including pre-sales, sales, support, shipping, etc irrelevant as
to who sent the email.

Obviously I don't want to reinvent the wheel or program my own fully featured email client, which I
would need to do if I wanted to convince users to stop using their Eudora, Thunderbird, Outlook, etc.

What I am hoping for is an email client back-end that can be loaded into a schema of an existing
database, and then the application would have access to the email data as well. The front-end would
need to have at least the commonly used components of an email client.