How can I limit the number of emails a domain can send out per hour?

Click on the "Tweak Settings" link under "Server Setup". Within the "Mail" section is a text box with the heading:

"The maximum each domain can send out per hour (0 is unlimited):"

Change the value and apply the changes by clicking on the "Save" button at the bottom of the page.

1st Aug 2020
Thank you for choosing WHMCS!

Welcome to WHMCS! You have made a great choice and we want to help you get up and running as quickly as possible. This is a sample announcement. Announcements are a great way to keep your customers informed about news and special offers. You can edit or delete this announcement by logging into the admin area and navigating to Support > ... Read More »

23rd Jul 2020