How can the encoding method, such as quoted-printable, affect the content of emails sent via PHP?

When sending emails via PHP, using encoding methods like quoted-printable can affect the content by converting special characters into printable ASCII characters. This can lead to issues with the display of the email content, especially if the email contains non-ASCII characters or HTML markup. To ensure proper encoding and display of email content, it's important to use the appropriate encoding method and set the content-type header accordingly.

// Set the appropriate content type and encoding for the email
$headers = 'Content-Type: text/html; charset=UTF-8' . "\r\n";
$headers .= 'MIME-Version: 1.0' . "\r\n";
$headers .= 'Content-Transfer-Encoding: quoted-printable' . "\r\n";

// Encode the email content using quoted-printable
$message = quoted_printable_encode($message);

// Send the email
mail($to, $subject, $message, $headers);