问题
I'm making a program which sends invoices to registered users as PDF attachment. Each invoice is identified by a GUID. In some circumstances I want to be able to find programmatically the GUID from mail without reading PDF file.
Can I use mail header field to include invoice GUID, or it is a bad practice and mail header fields are not for this purpose?
回答1:
It is common practice to use "X-HeaderName" to designate non-standardized headers.
来源：https://stackoverflow.com/questions/2115342/create-custom-mail-header-field