Unable to send email: "Domain example.tld has exceeded the max defers and failures per hour"

Symptoms

A domain cannot send emails, and an error similar to the following will be seen in the exim_mainlog log file.

2023-08-02 14:36:26 1qR7oJ-0006NK-0w ** example@external_example.tld R=enforce_mail_permissions: Domain example.tld has exceeded the max defers and failures per hour (5/5 (100%)) allowed. Message discarded.

Description

cPanel temporarily blocks a domain from sending email if the number of failed or deferred messages the domain has sent in the last 60 minutes is equal to or greater than the value of the "Number of failed or deferred messages a domain may send before protections can be triggered" setting in "Tweak Settings" and the percentage of failed or deferred messages sent during the same period is equal to or greater than the value of the "Maximum percentage of failed or deferred messages a domain may send per hour" setting in the account's account or package settings, or in "Tweak Settings." The temporary block will be lifted once the number or percentage of failed or deferred messages falls below the related setting.

Workaround

If the domain holder doesn't want to wait for the number or percentage of failed or deferred messages to fall below the related setting, the account's "Maximum percentage of failed or deferred messages a domain may send per hour" setting can be set to "Unlimited."

Please note that the source of the failed or deferred messages should be addressed instead of modifying the account settings.

1. Log into WHM as the 'root' user.
2. Navigate to "Home / Account Functions / Modify an Account."
3. Select the account to modify.
4. Click the "Modify" button.
5. Scroll down to the "Maximum percentage of failed or deferred messages a domain may send per hour" setting.
6. Select the "Unlimited (default)" option.
7. Click the "Save" button.
8. In the "Package Conflict Resolution" pop-up, enter a new temporary package name in the "Create a new package with this name" textbox.
9. Click the "Proceed" button.

Once the source of the failed or deferred messages has been addressed, the account should be moved to the previous package.

Additional resources

Tweak Settings: Mail

Edit a Package: Resource options

Modify an Account: Resource Limits

Improving Email Deliverability

How to Prevent Spam with Mail Limiting Features: Failed and deferred outgoing message options