Some helpful details regarding the Internet that are not specific to running an ISP.

To definitely be sure you receive mail from certain people you can do this:

1. Click on the gear icon at the top-right then choose Settings
2. Click on Filters and Blocked Addresses along the top
3. Click Create a new filter
4. Enter the e-mail address in the From box at the top
5. Click on Create filter with this search at the bottom-right
6. Check the box that says Never send it to Spam