You can customize the Outgoing Email Action layout by removing fields or making them read-only. However, keep the following considerations in mind because your adjustments can affect other areas of the layout or require you to populate other fields with content.
Required Editions
| Available in: Salesforce Classic and Lightning Experience |
| Available in: Group, Essentials, Professional, Enterprise, Performance, Unlimited, and Developer Editions |
Fields in the Email Message Layout
| Field | Consequence |
|---|---|
| Subject |
When you remove the Subject field from the layout, the Merge Field icon is hidden in the email composer. You can’t send emails unless at least one of these fields has content.
As the sender, you can provide the content, or it can be automatically inserted using predefined values. An email template can also include the content for these fields.  Note When you also remove the HTML Body field from the layout, the Insert Template
icon is hidden in the email composer.
|
| HTML Body |
When you remove the HTML Body field from the layout, these icons are hidden in the email composer:
You can’t send emails unless at least one of these fields has content.
As the sender, you can provide the content, or it can be automatically inserted using predefined values. An email template can also include the content for these fields. |
| Text Body |
You can’t send emails unless at least one of these fields has content.
As the sender, you can provide the content, or it can be automatically inserted using predefined values. An email template can also include the content for these fields. |
| Recipient (To:, Cc:, and Bcc:) |
You can’t send emails unless there’s at least one recipient. |