The subject line of the email sent Tuesday by Adidas Running read: "Congrats, you survived the Boston Marathon!"
On social media, customers quickly reminded the company about the real survivors of the 2013 Boston Marathon bombing. Three people were killed and more than 260 others were wounded when two bombs exploded near the finish line in that attack.
The sports apparel company quickly apologized, saying it was "incredibly sorry" for the "insensitive" subject line about Monday's race.
At least two survivors of the 2013 bombing participated in this year's race.
Adidas says the marathon is "one of the most inspirational sporting events in the world."