Hi,

There is a maximum of 5,000 emails that can be sent within a 24 hour period. This maximum is only available if you have Salesforce Unlimited Edition. ... Go to either the Leads or Contacts tab, choose mass emails under the Tools section, and use filters to create your email list.


From the salesforce docs:

Using the API or Apex, you can send single emails to a maximum of 5,000 external email addresses per day based on Greenwich Mean Time (GMT).


If you use SingleEmailMessage to email your org’s internal users, specifying the user’s ID in setTargetObjectId means the email doesn’t count toward the daily limit. However, specifying internal users’ email addresses in setToAddresses means the email does count toward the limit.


So if you are sending emails to internal users you may want to use setTargetObjectId of the SingleEmailMessage object instance.


Also, I hope you have bulkified your trigger to send all the mails of single transaction at once in the end.


=============================================

You're not easily going to be able to send that kind of volume with Salesforce alone. Sure, you can batch them up as you suggested, but then you will have potential scalability problems. What if you suddenly want to do two mailshots per month? What about any other emails you are sending - if you've used your SF allowance on these big batches, you might not have capacity for those.

If they are marketing emails, and you want to get into marketing automation, then consider using Marketing Cloud, or Pardot.

If you just want to send lots of email simply and relatively cheaply, you will need to make callouts to a specialist email delivery service. I've used both SendGrid and Amazon SES for these purposes. I slightly prefer SendGrid, but it's a bit of a matter of taste which is more appropriate.



Let me know if it helps you and close your query by marking it as solved so that it can help others in the future.

Thanks.