This is very simple to do.
1. Go to GMAIL online from your computer
2. top right hand corner click "Settings"
3. click "Accounts and Import"
4. set up all your other email accounts
5. on all account select option: Reply from the same address the message was sent to
This works perfect for me. I get all my emails on my main GMAIL account. Email addresses are all separated in there own email box and when you reply the email is sent from the same email address the message was sent to. I am using aol, company email, another gmail account, yahoo etc.. On the phone itself only set up your main GMAIL account that contains all your email addresses. You can set up your email addresses using pop, imap, smtp and exchange options. I get my emails almost instantly on all accounts.
I hope this helps you as much as it did me.
Enjoy your Android!