How to include PHP code in welcome email? I need PHP (for some logic) inside the welcome email, the welcome email structure is defined in admin/config/people/accounts (in the text box)

How can I place PHP code there? I tried to put some PHP but I only get a blank email. Or if I can`t execute PHP code inside the email box what module can I use to do this?
Updated :

Use PHP mailer module to send the email in the format of php