People submit my contact form but the emails never reach my inbox. What is wrong?

Contact form emails are only sent when the submission passes a reCAPTCHA check. Without one, the submission is still saved, but the email is held back to stop spam.

1. Go to Plugins → Recaptcha, tick Enable reCAPTCHA, add your Site key and Secret key, tick Contact & custom forms (Form Builder) under Where to show it, and click Save.
2. Go to Settings → Contact Forms and open your form. Add the Recaptcha field (in the Security group) and click Publish.
3. Click the form's settings gear, turn on Protect this form with reCAPTCHA on the Settings tab and click Update.

You can confirm the cause in Settings → Web Settings → Email Delivery Logs: held-back emails show Not sent — no reCAPTCHA.