To make sure Gmail never filters as spam mail from a certain contact or domain:

• Click the Show search options downward-pointing triangle in your Gmail's main search field.
• Type the desired email address under From.
  • To whitelist an entire domain (all mail from an address ending in "aboutguide.com", for example), type the just the domain name or the domain name preceded by '@'. To whitelist "aboutguide.com", for instance, type "@aboutguide.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 "jenny@example.com" and "jelani@example.com", enter "jenny@example.com|jelani@example.com", for example.
• Follow the Create filter with this search ›› link at the bottom of the search sheet.
• Make sure Never send it to Spam is checked.
• Click Create filter.