Gmail Spam Folder

Lately I have noticed that emails from SPH, Singtel, the Zoo, Night Safari, NLB have often been assigned by Gmail to the spam folder. Now NUS Alumni newsletter has joined them too.

I noticed they are all local. Meanwhile I get lots of unsolicited mail from e.g., Godaddy.com and others. None ever got sent to the spam folder save the obvious ones.

What gives? Why? Is there a white list of sorts?

I can no longer afford to summarily delete mail marked as spam by Gmail.