Enter SendHub, a startup in this year’s Y Combinator class, that has already started to get some serious traction by focusing on professionals. The company offers a clean interface for creating and organizing groups of people, and communicating back and forth with them over their desired format.

The result is that it has been growing fast. When Sarah Perez covered SendHub in February, the company was sending 30,000 messages a month. Now, it’s sending around that amount per week. Check out the graph below. The numbers are still small, but they’re in the right direction. YC partner Paul Graham says that its growth looks like AirBnB’s in the early days.