Messages that never arrive.
THE MOST COMMON CAUSE
The application uses PHP's mail function by default. Messages sent that way frequently fail authentication and land in spam.
THE FIX
Configure the application to send through SMTP using a mailbox on your domain.
Host mail.yourdomain.com, port 465 with SSL or 587 with TLS, authentication enabled, the full address as username.
THE FROM ADDRESS
Must be on your own domain. A form sending from the visitor's Gmail address fails authentication and is the most common reason submissions disappear.
Put the visitor's address in Reply-To instead.
CHECKING WHETHER IT LEFT
cPanel > Track Delivery shows whether a message was sent and what the receiving server said. This settles whether the problem is at your end or theirs.
AUTHENTICATION RECORDS
Confirm SPF and DKIM are correct under cPanel > Email Deliverability.
SENDING LIMITS
Shared hosting has hourly limits. An application sending in bulk will be interrupted.
TESTING
Send to Gmail and another provider, and read the headers for authentication results.
