▲四家钢铁企业近十年毛利率走势图，来源：Wind
Фото: Kevin Lamarque / Reuters
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What are the best deals at Amazon's Spring Sale?
If the subject line of the email is irrelevant to customers, they will ignore it multiple times. But, if it keeps repeating, they are intercepted and unsubscribed from your emails. So, send relevant emails for the benefit of the customer. Don't send emails that often only focus on sales, offers and discounts.