For a myriad of reasons it's nice to know what IPs you can expect to see coming to/from your Azure space. Below is a quick cheat sheet.
Microsoft Azure Datacenter IP Ranges (Commercial)
Microsoft Azure Datacenter IP Ranges (Government/Sovereign Cloud)
upon request; please open a case via the Azure ARM (new) Portal
Office 365 URLs and IP address ranges
Office 365 US Government: Endpoints for US Federal and US Defense Clouds (preview)