Salesforce Email Body Character Limits — Send Email vs. Case Feed Publisher

This article explains the email body character limits in Salesforce and how they differ depending on which method is used to send email.

Standard Email — Send an Email Button (Classic UI)

The standard email body field supports up to 384,000 characters when sending or composing an email using the Send an Email button from the Emails or Activity History related lists in Classic UI.
If this limit is exceeded, the following error displays:
"Error: You can't send emails with body content that exceeds 384,000 characters. Shorten your email and send it."
The recipient receives the email with up to 384,000 characters regardless of the organization's default email body character size limit.
 Refer to the field limits for an email body (EmailMessage) on page 173 of the Field Reference Guide for more information.

Email Publisher Action — Case Feed and Lightning Experience (LEX)

Lightning Experience (LEX) is Salesforce's modern browser-based user interface. When using the email publisher action in the Classic UI Case Feed or LEX UI, users cannot enter more than the organization-level email body character size limit.
The default organization limit is 131,072 characters. This is a hardcoded limit that Salesforce Support cannot increase manually. 

To learn more about the error you receive if you exceed the limit and workaround options, review Error 'You cannot use more than 131,072 characters' when sending emails using the Case Feed Publisher or Global Email action on LEX.  

Truncation Behavior After Sending

If an email is sent from the Emails or Activity History related lists with more characters than the organization's default limit (131,072), the email copy stored in Activity History after sending is truncated to the organization's defined limit.

HTML and Character Count

All HTML code and new line characters count toward the email body character limits. Simplifying the HTML in the email reduces the total character count. Emails pasted from external editors such as Microsoft Word often carry over unnecessary HTML markup.

Troubleshooting Tips

• Test in another browser or use Incognito mode when the email cannot be sent. A browser extension may be adding HTML content to the email, increasing the character count beyond the limit.
• Turning off browser extensions one at a time can help identify which extension is causing the issue.