You can only send 250 DMs from one account per day:
On Jul 28, 2010, at 12:47 AM, Mark Sievers wrote:
> Kind of curious what would happen myself. The call is not itself rate-
> limited, and the target must be following you (ie they have opted in)
> so this is ok, but wonder if firing off 1600 DMs in the space of a few
> minutes raises any red flags in the Twitter mopther ship.