The trick is to use Gmail’s filter feature. Gmail supports filter to apply certain action on rules-matching incoming mail, and the filter can be created in order to force all email received to skip been sent to the Spam folder and remain in the Inbox (which is downloadable via POP3 or IMAP). To create a filter to disable or deactivate the spam filter in Gmail, click on Create a filter link beside the search box (or go to Settings -> Filters -> Create a new filter).
In the Has the words: text box, enter one of the following terms:
is:spam or in:spam or label:spam
Click on Next Step button, and click on OK button when a dialog pops up to warn against using in:, is: or label: criteria in filter.
Check and tick the checkbox for Never send it to Spam as the filter’s action. Click on Create Filter to disable and deactivate the Gmail spam filter with immediate effect.
Although from now on no spam messages will be sent to Spam folder anymore (everything stays in Inbox), Gmail is still smart enough to warn users that an email is identified as spam, but stays in Inbox and not send to Spam folder due to the filter created.
