Are e-mails legally binding?

I work with a person in the entertainment industry. His job is very physical and recently was asked to show training tips in his field to another entertainer for a 2-page-spread in a popular magazine. The magazine contacted me and him through a website we run and offered to give the site and him promotion in exchange for his help. This would mean being credited in the magazine, the on-line article, and the magazines social media accounts. All this was said in various e-mails. Towards their deadline, they e-mailed and reconfirmed how things would be credited in the magazine and site. A few months later, the article was out and then a week later posted on-line. There was no mention of the promised promotion and they didn't even credit the person I work with. Does the e-mails have any legal weight? We aren't necessarily going to take any legal action, but I have yet to contact them about this and wanted to know what weight an e-mail had.