If you do not want that the mails coming from a particular sender are tagged as a spam, then you can follow the various steps:
>> Click on the gear icon. It is situated in the upper right corner of your window.
>> After then, select the tab “settings”.
>> Click on Filters >> Create New Filter.
>> Fill the details of a person’s address in the “Form” field.
>> Click on the option “Create filter with this search”.
>> Select the option “Never send it to spam”
>> Click on the option “Create Filter”.