How do I prevent email that I want to receive from being marked as spam?

If messages that you want to receive have been sent to your spam folder, you can prevent that from recurring by taking three steps:

1. First, you should add any important addresses to your Contacts List. Most messages from people in your Contacts List will be delivered.
2. Then, you should review the contents of your Spam folder and mark messages you want to receive as NOT SPAM. Gmail’s spam filtering system will learn what you think is spam based on what you mark as spam and not spam. It will change how future messages are filtered based on that.
3. Finally, you can create a filter so the messages are never sent to the Spam folder.