Printing and Postage

I have some low quantity direct mail letters that I want to print and mail. They are sales letters that I've written for follow-ups.

Can anyone recommend any online printers that allow you to upload your file and they'll print and mail in less than 1,000 quantities?

All the sites I come across will print letter head and ship the entire order to my address.

I'm looking for a mail shop that I can just upload my docs and my mailing list and they take it from there.

Thanks
Matt