I'm writing a bill generation service for a client, and I would like to program my self out of the most time consuming part of the process. It goes something like this. 

> 
> print X number of pdfs and envelopes, stuff envelops, stamp, and bring to post office 
> 
> 
> 

It would only be a few hundred bills monthly to start but it could grow. I'm sure some sort of service exists that provides an api to deliver a printed pdf to an address but I can't find one. I think part of my problem is discovering the terminology to google with.

Have you ever used any services like this?

**UPDATE**  

I've found some helpful search terms, but no good results yet.

> 
> Mail Processing Services  
> 
>  Document Processing Services
> 
> 
> 

I should also add that I'm located in nyc and am looking for a US based solution.