Bluetooth connection to the Era 100 would be easiest. You’d use whatever player you have on the Android device to play the attachment, and it would travel via Bluetooth to the Sonos. 

Thanks for the reply. I already have a Bluetooth connection. The problem is that when I go into Gmail mp3 attachments it synchs to a sony remote speaker which I also use. Do I have to give up one of the connections to use the other one or can I switch between the two?

That would be an Android question, not one I can definitively answer, sorry. 

My understanding of Bluetooth (although I use it from the Apple side), is that it’s an ‘all or nothing’ connection, and things are not able to be driven from one output (Bluetooth) to another (non-Bluetooth). I think you have to choose one or the other.

As Bruce said I think this is a question for Android but in some cases the "premium" phones have a function to send the audio via Bluetooth up to 2 devices at the same time but to have a better result the must be the same brand or CPU, in this case when I use this function with my S23 with all products I own and using a Era 100 or a Roam I think they are adaptative so the sound is sync but I think that info is in the manual of your phone :)

It’s possible that Android has a capability to push audio to different ‘points’, but I was under the impression that Bluetooth was an OS level connection, and not a ‘per source’ connection, which would mean all ‘sound’ coming through the OS would be sent to Bluetooth. 

It was before now you can also select which apps you want to listen on your phone and which in the Bluetooth device :)