I have a new installation of Zen Cart 1.5.4.
PHP 5.6
memory_limit 128M
site: http://lanterncove.com.au/
host: uberglobal

I have tried PHP, sendmail, smtp and smtpauth, only sendmail partially works.

All admin emails are received ok.
The Email Archive logs all emails ok.
If I send a direct email from within the admin console, it arrives ok.
I uploaded the email_test plugin and that worked fine.

However, new registration emails, order confirmation emails and the newsletter emails do not arrive at the destination.

Do you have any suggestions as to what I can look into to see what the problem might be?
Thanks