To ensure reliable deliver of email from your website, there are some best practices to observe.
In Backlight's Settings:
In most cases, your Mail Send Type should be set as "mail" in Backlight's settings.
Also in Backlight's settings, your Site Email and Vendor Email should be an email address that matches the domain of your site, i.e. @yourdomain.com.
Your host should be aware of the above email address; create an email account in your host's control panel matching the sender's access. You do not need to use the host to manage the email 1, but this makes the host aware of it being a valid address, so that it will trust Backlight's attempts to send mail using the address.
- ... which would require updates to your DNS.↩