Shaunmac here's a few links to Stamps.com US regulatory filings to enable you to DYOR here on the competitive landscape here.
The 10-K for fiscal 2017 should be out in early March which generally provides a far greater level of detail than the 10-Q's on operating matters and the market in general.
I find that these 10-K filings provide a great way to do some basic due diligence when DYOR
Off the latest 10-Q Stamps.com has the following math :
Revenue (annualised) of US$460m
Operating cashflow (annualised) of US$198.7m
EBIT (annualised) of US$142.6m