I'm not positive you can email the registration applications. They may require an original signature, but I am going to find out.
If you go to AMHA's website, go down the list of links on the right side of the page to where it says contact AMHA and click on that. It will bring you to a list of email addresses for the AMHA office. Under registration, I send mine to Marsha who handles registering new foals.
I know that you can email registration applications and pictures to PtHA as I have done that this year.