When a user fills out a form on a PHP web page and clicks submit, the PHP code on the server receives the form data and can use it to send an email to the designated recipient(s) using SMTP (Simple Mail Transfer Protocol).
SMTP is a protocol used for sending email messages between servers. When sending an email using SMTP, the sending server establishes a connection with the recipient's email server and sends the email message over that connection.
In the context of a PHP web form, the PHP code on the server would use an SMTP library or function (such as PHPMailer or the built-in mail() function) to send an email using SMTP. The code would typically specify the sender's email address, the recipient's email address, the email subject, and the email message body.
The SMTP library or function would then handle the process of establishing a connection with the recipient's email server and sending the email message over that connection. Once the email has been sent, the user who submitted the form would receive a confirmation message indicating that their message has been sent.
It's worth noting that the specifics of how this process works can vary depending on the hosting environment and the email service being used. For example, some hosting providers may restrict the use of certain SMTP libraries or functions, and some email services may require additional configuration or authentication steps to send emails via SMTP.