How to limit emails sent per hour

Introduction

In order to prevent a compromised account from sending large amounts of spam and damaging the reputation of the server, it can help to limit the number of emails a domain can send per hour. This article provides the steps to set this limit.

Warning: The maximum sending rate is the number of emails each domain on an account may send per hour, not the total number of emails sent from the account per hour.

Procedure

1. Log into WHM as the root user.
2. Navigate to Home / Server Configuration / Tweak Settings / Mail 
3. Locate Max hourly emails per domain and set your limit. 
4. Navigate to Home / Account Functions / Modify an Account.
5. Select the account to modify.
6. Click the Modify button.
7. Scroll down to the Maximum Hourly Email by Domain Relayed setting.
8. If the Unlimited (default) option is selected, select the textbox option.
9. Enter the maximum number of emails you would like each domain under this account to be able to send per hour.
   Warning: A value of 0 will be interpreted as no limit.
10. Click the Save button.
11. Enter a new package name in the Create a new Package with this name textbox.
12. Click the Proceed button.

Warning: When a domain reaches its limit, the system does not block additional messages at SMTP time. Instead, the system accepts and then handles additional messages per the value of the "The percentage of email messages (above the account's hourly maximum) to queue and retry for delivery" setting in "Tweak Settings."

Additional resources.

Modify an Account

Tweak Settings

How to Set Email Send Limits