Hi Tom,
Welcome and thanks so much for reaching out!
The server that is used to send emails is the WordPress server. Sometimes for unexplained reasons, things just don’t work properly at one time or another. If you test again and things still aren’t working properly, you do have another option.
You can have the system send tickets from any chosen email address by simply installing, configuring and testing the following plugin: https://wordpress.org/plugins/easy-wp-smtp/
Using a real SMTP server with authentication will bypass the built-in WP mail functionality altogether.
Please make sure you configure and test the settings using the plugin’s built-in tool.
Let me know how it goes and if you have any other questions on this topic!
Thanks,
Jaime