To make sure Gmail never filters as spam mail from a certain contact or domain:
- Follow the Settings link in Gmail.
- Go to Filters.
- Click Create a new filter.
- Type the desired email address under From:.
- To whitelist an entire domain (all mail from an address ending in "about.com", for example), type the just the domain name or the domain name preceded by '@'. To whitelist "about.com", for instance, type "@about.com" (not including the quotation marks).
- You do not have to create a separate filter for each address. Separate addresses with '|' in the From: field instead. To whitelist both "email@example.com" and "firstname.lastname@example.org", enter "email@example.comfirstname.lastname@example.org", for example.
- Click Next Step ››.
- You can click Test Search before, of course, to make sure you did not mistype.
- Make sure Never send it to Spam is checked.
- Click Create Filter.