That sounds really complicated. Wouldn't you just use something like Syncthing to synchronize your org mode files across devices? I use Orgzly and Syncthing in my phone and it's good enough.
If you use it for general email stuff, just have a Cron job pulling your email down and append new stuff to a file that gets synchronized.
I don't really get why AWS, S3, or lambda are involved, unless you just wanted to see if you could do it.
I definitely used it as an exercise to learn lambda. I don't have an android phone for orgzly and at the time of creation, there weren't any solid iPhone org-mode apps.
I use org-brain on the backend and the lambda function does some processing to automatically categorize and such.
If you use it for general email stuff, just have a Cron job pulling your email down and append new stuff to a file that gets synchronized.
I don't really get why AWS, S3, or lambda are involved, unless you just wanted to see if you could do it.