Why am I unable to send an email order using the Ubercart and Smtp Authentification module? After Ubercart checkout submitting order, I get this error:


  Unable to send email. Contact the site administrator if the problem
  persists.


I am using the SMTP Authentication Support module, I configured it correctly. Test mails work. So the error lies probably within Ubercart.

On Drupal /admin/reports/dblog, I get this interesting error log:


  Error on sending e-mail (from admin@xxxxx.com to
  admin@xxxxx.com.com).


it tries to send the mail to the sender mail? Very weird!

How to get this resolved?
Okay I found the solution using the instructions at "Drupal – Ubercart and SMTP Authentication Support".


I installed Mail System module.
In the Mail System configuration, I updated the Cart module class, Order module class and Store module class so that they all use the SmtpMailSystem rather than UbercartMailSystem, as shown in the screenprint below: