What is the importance of properly encoding emails in PHP applications?

Properly encoding emails in PHP applications is important to ensure that special characters are handled correctly and prevent potential security vulnerabilities such as email header injection attacks. To encode emails in PHP, you can use the `mb_encode_mimeheader()` function to encode the email subject with the correct character set.

$subject = 'Subject with special characters like é and ü';
$encoded_subject = mb_encode_mimeheader($subject, 'UTF-8');