Carolyn,
I've not had any problems submitting paperwork to either registry by email. You need to make sure that all forms sent are complete including signatures. Pictures attached should be just like they would if you were printing them out, ie, all body parts showing and the horse covering approximately 80% of the picture as per registry requirements.
The only problem I've encountered this year with a new registration, is one foals' name in AMHR couldn't be used as I sent it, as the last word is a registered suffix with another farm. Fortunately for me, AMHR called me on the phone, I came up with a solution and the papers were sent to me and I had them in my hands in a few days. No long delays snail mailing paperwork back and forth!
I generally try to send pictures that are under 100kb so I can attach 4 to an email and have them go through without any problems.