Spam is classified by many factors - if you send out many similar, unasked for emails for recruiting, Gmail users will mark them as spam, which then blacklists your domain on Gmail. Please do not do this to reach out to people, but use other methods than email!

ah ok, that's exactly what I was doing! Not spam emailing, but researching to see what local businesses or groups might be interested in our club. We'll try another way!