When sending email to Gmail (or some other service), delivery fails with the following message:
This message does not have authentication information or fails to pass authentication
checks. To best protect our users from spam, the message has been blocked. Please
visit https://support.google.com/mail/answer/81126#authentication for more information.
The error follows recent (middle 2019) measures that Google put in place to curb domain spoofing and spam. The solution is to add email authentication records to your domain's DNS in the form of SPF and/or DKIM records.
To add SPF and/or DKIM records, use the Email Deliverability function in your cPanel. Depending on how you send email for your domain, several options are available to you.
If you send all email for your domain through our server:
Enable both the SPF and DKIM options. The default settings will suffice, but you if you never send email through any other server, then you can also use the option to "exclude all other hosts".
If you send some email for your domain through other servers:
Your SPF and DKIM records must include reference to all server that send email for your domain. If you are using MailChimp to send newsletters, for example, then you should include their servers as outlined at https://mailchimp.com/help/set-up-custom-domain-authentication-dkim-and-spf/. In this case the DKIM configuration can be tricky and you may want to avoid it altogether and use SPF only.
For additional information on authentication and preventing email spoofing, also see the following article: