If you've set up more than one email account on your tablet, you need to select a default email account. When you write email, they'll automatically be sent from your default email account.
Step 1 of 5
Find "Default Account"
Tap Settings.
Step 2 of 5
Find "Default Account"
Tap Mail, Contacts, Calendars.
Step 3 of 5
Find "Default Account"
Tap Default Account.
Step 4 of 5
Select default email account
Tap the required email account until it has been selected as the default email account.