If you find that your emails are not sending out to your customers and that they display a Delivery Failed error, please make sure you have not entered an actual email address in the Send emails from (name) box, which can be found in the Emails & Texts section of your site settings.
To check this, you will need to:
Click Settings, Sites, and select the site.
Click Emails & Texts.
Make sure that the Send emails from (name) box does not contain an email address but the actual site name.
If the Send emails from (name) box contains an email address, please remove the email and replace it with the site name.
Click Save.