1, check from the Sender, that’s the Email address send from. Generally, if it is from a real business, you can find many related information related with the email. Otherwise, if this email have scammed somebody before, there should have a record in Google search results. You can go directly to the website if you copy the part right after the @ symbol of the email if the sender is a real business, otherwise, if it is spam, there is no website.

2, Check from the content, the more generic inquiry the bigger percentage of spam. A clear sign of the spam email is the content hasn't a specialized reference for the product. They just asking your price list, catalog, delivery time, etc. If the sender of the email is a hacker, they generally including an attachment in Zip, pdf, exe, html file, please don’t open it, and only open pdf, jpg, word, excel files until you verified the sender is a real business such as email address can direct to an authentic website. 

3, Sender using free emails such as hotmail, gmail,yahoo.com, 163.com can be a real business, as many business owners prefer free mails for more privacy. You can verify it through the contact information provided in the email footer, and also from the email content. Real business showing expertise writing their product, expressing their buying request, email content is very specific and clear. 

4, promotional emails are not spam email. As far as promotional emails are related to authentic products, services, not drugs, and criminals, the sole purpose of the sender is to solicit buyers which is like solicit buyers alongside the street. If senders send the email to the right one, most probably they’re sending from an email campaign.