Sure, Gmail's spam filter is mighty and good. When you visit the Spam view, all you see is junk. All the mail you want to receive arrives in time.
What, though, if you want to be sure — sure that messages from your peers, your friends or your family never end marked as spam by Gmail? That security is in a filter that's simple, effective and set up easily.
Whitelist a Sender or Domain in Gmail
To make sure Gmail never filters as spam mail from a certain contact or domain:
1. Click the Show search options downward-pointing triangle in your Gmail's main search field.
2. Type the desired email address under From.
3. To whitelist an entire domain (all mail from an address ending in "example.com", for example), type the just the domain name or the domain name preceded by '@'. To whitelist "aboutguide.com", for instance, type "@example.com" (not including the quotation marks).
4. 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.
5. Follow the Create filter with this search ›› link at the bottom of the search sheet. Make sure Never send it to Spam is checked.
6. Click Create filter.