Hello and welcome to Apple Support Communities, mwblum!
I understand that Mail app is defaulting to the incorrect account. I'd be happy to provide information on how you may resolve this.
I believe you've been looking at the following article: Add an email account to your iPhone, iPad, or iPod touch
What you'll want to do is go to Settings > Mail and scroll to the bottom to change the default account.
If I've misunderstood your issue, please reply with any additional information you can provide.
Thank you for using Apple Support Communities.
Enjoy your day!