Redmine

Hi everyone.

I'm really new to the whole redmine topic, so i hope you guys can help me out.
Our company has redmine installed. We have a mailserver which contains all our received emails (from customers etc.).
It's pretty simple to select an email via sql query, since every mail has a primary key.
What i'm trying to achieve is adding a custom field (when creating an issue) in which you can put a primary key in.
The primary key should be handled to a script (tcl, python) which returns the mail-body of the selected mail.
So it's like hyperlinking a key to a file which connects with our database and returns a text in xml format.

I'm really frustrated right now, hope you guys can help me out.
Is it right to have an api between redmine and our database? Is there a better way to solve this?

This is the scenario i want to accomplish with my plugin: ISSUE[name, ticketnumber,....EMAIL-ID]. EMAIL-ID > should be passed to my BACKEND-SCRIPT. BACKEND-SCRIPT>uses the passed EMAIL-ID to find mail and returns found EMAIL-BODY as xml (or a simple string?).

Do i even need to make a plugin for this?