Adding include in html email

Hi, since fopen is no longer an option, does anyone know how to add an include (ie. a .txt file) to an html email?

We send out emails to our students that also has a schedule that changes week to week, so if the student opens it up after that week, it needs to be the newest schedule. Is this even possible?

thanks

using the curl method worked. Thanks for a great read to whomever wrote it!