This has been a gripe for a long time. I have multiple email accounts. When I create a new (not a reply) email the program takes the To: address of the currently viewed email as the From: address in the new email. This has caused me grief in the past.
Outlook on my PC and the 3rd party email program I use on my Android allows me to define a default account/From: email address.
Outlook on my PC and the 3rd party email program I use on my Android allows me to define a default account/From: email address.