My organization is also trying to solve a problem like this, and I can share with you some of the things I found. We are not doing this yet, still at the design stage, so consider the following.
Your situation also depends on the required format in the post office - at the moment they have to accept Word 97 documents, can they also accept XML, DOCX, PDF or something else?
There is a commercial product called Intelledox , which allows you to use Word 2003 (perhaps already in Word 2000?) As a template designer and then collect documents from data sources, which can be databases, web services, etc. It seems like a pretty interesting product depends on your budget. This is likely to be highly rated by your criteria for the design of end-user templates.
You can see the Open XML SDK , which allows you to programmatically create DOCX files (Word 2007). Your business users will generate the template in Word and provide it to the developer, who will then likely create XSLT. This XSLT is then used at run time to programmatically replace the contents of the basic template of a Word document. This does not require Word on the server, but only the .NET libraries that are part of the SDK. The disadvantage of this is that when creating a new template, a little processing by the developer is required.
I also looked at the reporting approach β we use SQL Server Reporting Services and can use it to create a federated document. It supports Word, Excel, PDF and other export formats. The disadvantage of this is that it usually requires a developer to develop a report. You can deploy SQL Server Reporting Services Builder , which is designed for advanced users to create their own reports. If you are considering this approach, make sure it is SQL Server 2008 (Report Builder 2.0), obviously Report Builder v1.0 is pretty poor.
If the mail service accepts XML, you can provide the mailbox to the XSLT file and simply send the data, not the assembled document. Not sure if the print house you are using accepts this, or if you need to keep a copy of the completed document internally for audit purposes.
Finally, it might be worth a look at the XPS format . Not sure how the templates will be designed for this, it may be too hard for programming.
Hope this helps with your thinking!