I had the same problem (the “send” button on the backup email was grayed out) and I finally got it to work. I did two things at once so I cannot day for sure which one solved the problem: 1) I installed the Apple iPhone email app on my phone, 2) I reduced the number of my contacts to less than 500. I believe installing the Apple mail app did the trick because before I did not notice a “from” email address in the back up email. After I installed the app, my email address was in the “from” field and the “send” button turned blue.
I had the same problem (the “send” button on the backup email was grayed out) and I finally got it to work. I did two things at once so I cannot day for sure which one solved the problem: 1) I installed the Apple iPhone email app on my phone, 2) I reduced the number of my contacts to less than 500. I believe installing the Apple mail app did the trick because before I did not notice a “from” email address in the back up email. After I installed the app, my email address was in the “from” field and the “send” button turned blue.