The spam folder in GMail is always hidden and it becomes more and more uncomfortable How to configure GMail Spam folder to be always visible?
closed as off topic by Lèse majesté, John Conde♦ Jan 28 '11 at 12:49
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To whitelist individual email addresses:
Settings -> Filters -> Create a new filter. Fill in the emailaddress in the "From" field, click Next, and select "Never send to spam". Instead of an entire emailaddress you could use a partial address too, like @yourcompany.com to whitelist all mail from that domain name.
You can also just pick a mail from the spam box and click the button "Not spam". If you do this a few times for the same sender their mail will start ending up in your inbox too.
To always show the spam box:
Settings -> Labels
In the first list (system labels) look up 'Spam' and click the 'show' link next to it. Here you can set show/hide settings for all your other labels as well.