Direct Messages, or DMs, in Twitter are like private tweets that are visible only to the sender and the recipients. When you send a Twitter DM to another user, the tweet shows up in his Twitter Inbox while a copy of that message gets saved to your Sent Items just like email.
Twitter lets you send direct messages to any other Twitter user provided he or she is following you. The other limitation is that, unlike email, you can only send one direct message at a time.
There are situation when you want to send private DMs to multiple people on Twitter. For instance, it’s your birthday and couple of people have sent you birthday greetings through public tweets. Now you can either thank them all with public tweets (@replies) or you can send them private DMs containing the same note.
It’s simple. Just authenticate the app with your Twitter account and type the Twitter handles of all the users whom you want to message (see screenshot). You can use TweetGuru to send direct messages to 12 different users at a time.