Whmcs Email Sending Failed - Invalid System Template Name

Invoices generated but not sent - client not receiving invoice email
WHMCS Error: Email Sending Failed - Invalid System Template Name



cron System Activity Log

Email Sending Failed - SMTP Error: Data not accepted. (User ID: 91 - Subject: Customer Invoice)

System Theme The theme you want WHMCS to use
The error occur because of custom template director within /whmcs/template.

To resolve the error:
Rename the custom template directory name, it should contain only numbers and letters.
Then go to WHMCS admin panel -> Setup -> General Settings -> General Tab -> Template, re-select template name and click Save Changes.


System emails are sent via PHP (unless you are using SMTP) so it will come down to how you have PHP and mail configured.


This error message indicates that your mail server has been changed to not allow emails to be sent from an address which doesn't exist. Check the email set in General Settings > Email Address and General Settings > Mail > System Emails From Email are both pop3 accounts which exist on your mail server