This is an example. The business is fictional. A free health check using public information only: the same things any visitor's browser or email server can see.
Anyone following an https:// link sees a full-page "Your connection isn't private" warning. Most people leave at that point. It's usually a free fix from your host.
These are extra instructions that tell browsers to protect your visitors. Adding the rest is a small, one-off change.
Your domain lists who is allowed to send its email.
DMARC tells Gmail, Outlook and others what to do with fake emails using your name. Without it, scammers can send emails that look like they're from you.
DKIM adds a digital signature to your emails.
The site adapts to small screens.
Faster sites keep more visitors and rank better on Google.