How to pass hidden data in php email subject line?

Question

As I want to handle email failure and in that case when you send mail to other and if it gets in failure because of invalid to-email or etc. reason. In that case I can't see my email body in failure but I can see only subject line. So for that I want to pass hidden data in php email subject line.

Answer 1

that is not possible to pass hidden data in subject line

Answer 2

There is no way to hide data in the E-Mail subject.

The best you can do is include a code, and store additional information about this code in your database. When you are returned an E-Mail, you can use the code to look up the data.

That's the way many support systems work. The messages they send out will be in the form

(#1234567) Your support request

they are then able to parse out the 1234567 and look up the info, associate the reply with a customer, etc.