You receive the following error when adding a new comment and sending an email.  The comment is added but the email is not sent.

 

When these types of errors occur, you have exceeded your organization's daily single (outbound) API/Apex email limit. You can email a maximum of 5,000 external email addresses (non-users*) each day via the API/Apex, regardless of your Salesforce edition. This limit resets each day at midnight GMT. Unfortunately, this limit does not scale with user count like most SFDC limits.  Please note that this limit applies only to outbound emails; inbound email limits scale by 1,000 emails per Salesforce user license (up to a maximum of 1,000,000 messages per day).

 

Emails sent via the standard Salesforce UI through the Send an Email button (not E2CP), Workflow, Flow, Process Builder, and Auto-Response Rules do not count against this limit. 

With the New Comment Page, Email to Case Premium uses 'setTargetObjectId()' and sends emails from Contact records, which counts against the daily single email limit. Email to Case Premium uses a Flow for the Scheduled Comments feature to send emails, which invokes APEX and also counts toward the daily single email limit.

 

To summarize, any email sent by Email to Case Premium will count towards your daily single email limit.  This includes:

• all emails sent from the New Comment Page
• any emails sent as part of Email Distribution
• any email sent using the Invocable Method (Send Email action) 
• This is all true, regardless of whether the recipient is a contact or internal user

 

Frequently Asked Questions (FAQ):

• If internal users are exempt, why does including them on outbound emails count towards our limit?
  • Because E2CP resolves the User's email address and places it in the To/CC/BCC recipient fields, it cannot directly reference the UserID to qualify as exempt.
• If one email is sent using E2CP, and it includes 10 recipients within the To/CC/BCC lines, how many emails does this count as?
  • This counts as 10 emails for your single daily limit.
• If you include the same email address 3 times in an email, does that still count as 3 separate emails (as far as the limit is concerned)?
  • No, this would count as one email. The email limit didn't used to take unique email addresses into account, but it does in this sort of situation.
• If you email the same email address 3 separate times (not include its email address 3 times in the same email, as described above), how many emails does this count as?
  • This counts as 3 emails for your single daily limit.

 

To increase this limit or for clarification, please contact Salesforce.com Technical Support.  If you need to escalate the matter, contact your Salesforce.com Account Representative.

For more information, please see these Salesforce knowledge articles:

 

• Overview of email limit types
• Single email daily limits for messages sent using API methods
• Check the SingleEmailMessage limit