Email Body Section Doesn't Load in Lightning Experience Email Composer

The root cause of the Email Composer body not loading is the Block third-party cookies setting in Google Chrome. Salesforce Lightning Experience requires third-party cookies to be allowed in order to render the Email Composer body section correctly. Third-party cookies enable Salesforce components to communicate across frames within the browser, and blocking them prevents the body area from loading.
To resolve this issue, disable the Block third-party cookies setting in Chrome:

1. In Google Chrome, click the three-dot menu in the top-right corner and select Settings.
2. Navigate to Privacy and security > Cookies and other site data.
3. Select Allow all cookies, or add your Salesforce org domain (for example, yourorg.lightning.force.com) as an exception under Sites that can always use cookies.
4. Close and reopen Google Chrome, then log in to Salesforce Lightning Experience again.
5. Navigate to a record and select the Email tab to confirm the Email Composer body now loads correctly.

Note: If you are on a managed or corporate device, your Chrome cookie settings may be controlled by your IT or security policy. Contact your IT administrator if you are unable to change cookie settings.
. See Too many redirect errors and blank pages in Google Chrome on how to allow third-party cookies.


See also:
Email body does not display in Lightning UI, when you insert a template in the Email Composer
Recommendations and Requirements for All Browsers