const regex = /[^m]>/g;
// Alternative syntax using RegExp constructor
// const regex = new RegExp('[^m]>', 'g')
const str = `<test@gmail.com>
>Lorem ipsum dolor sit amet,<test@gmail.com> consectetur
>adipiscing elit. Integer nec >
>odio. Praesent libero. Sed cursus ante dapibus diam. Sed nisi. Nulla
>quis sem at nibh elementum imperdiet.Duis sagittis ipsum. Praesent
>mauris. Fusce nec tellus sed augue semper porta. Mauris massa.
>Vestibulum lacinia arcu eget nulla. Class aptent taciti sociosqu.
<test@gmail.com>`;
const subst = ``;
// The substituted value will be contained in the result variable
const result = str.replace(regex, subst);
console.log('Substitution result: ', result);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for JavaScript, please visit: https://developer.mozilla.org/en/docs/Web/JavaScript/Guide/Regular_Expressions