Hey,
I have built many bots/automated solutions for Twitter, Instagram, Facebook, YouTube, and many other social platforms over the years. I have over 10 years experience as a software developer, and a reverse engineer. I have built Twitter retweet bots, private messaging (dm'ing) bots, and anything inbetween that you can imagine in the past for previous employers.
I am very confident that I can provide you with with a top-notch Twitter messaging Windows Desktop Application where you feed it accounts, a list of people to send the direct messages to, and it will automate your entire process. The application will of course have proxy support, spintax for your direct messaging, and not to mention I will build it using the latest and greatest, top-of-the-line technologies including parallel programming. That way, your application is extremely efficient and entirely performanced based, BUT... with human-like behaviour features implemented if you need them.
However, I would love to hear some more information regarding your project as I am unsure if it's an automated solution (bot) you are looking for. Either way, I can take care of this for you with my experience.
I hope to hear from you soon buddy,
CreatedAutomated