Automatic selection of account based on recipient
The default mail app has this cool hidden trick: when you add the first recipient it will switch the account to the one previously used with this recipient. It's super useful. Of course, you need to show the used account in a clearer way.
Samuel Kordik commented
This would be especially helpful since I have two work and one personal accounts. One work one is almost entirely used internally, I.e. all recipients have the same domain name as my email for that account.
Ali Sakr commented
Please add this feature. It's in the iOS email and is very useful especially for users with several accounts.