Which service are you using? Adobe Send or SendNow? (We don't have anything called SendmeNow.)
For SendNow, which is about to be retired, the limit is 2GB.
We're currently experiencing problems with large-file uploads to Adobe Send (our newer service), so I would not be surprised that a 5.7GB file fails to upload. At this point, we don't have a hard date as to when this will get resolved (which is one reason why we have not yet disabled SendNow).