The subject of the email reads: "Congrats, you survived the Boston Marathon!"
Several people who received the email tweeted pictures of it, prompting widespread outrage.
Critics slammed the wording of the email as insensitive in the wake of the 2013 bombing at the Boston Marathon that killed three people and wounded dozens more.
In a statement to Business Insider Tuesday afternoon, Adidas apologized for the email's subject line.
"We are incredibly sorry," Adidas spokeswoman Maria Culp said. "Clearly, there was no thought given to the insensitive email subject line we sent Tuesday. We deeply apologize for our mistake. The Boston Marathon is one of the most inspirational sporting events in the world. Every year we're reminded of the hope and resiliency of the running community at this event."