It happens to the best of us. We spend large chunks of time developing, writing and formatting an email or a newsletter only to realize after it has already been sent that a mistake has been made.
An email marketing error that is common and easy to make is a spelling or grammatical mistake. In order to avoid making such mistakes, you can start using Grammar.ly. However there are other mistakes too that you can make such as the design on the email body, UX of a landing page where you want the visitors to land, broken links, or simply some backend issue.