We've talked before about adding a new account or deleting an account, but now we're going to talk about changing the order of accounts.

Go to Menu > Tools > Accounts. On the left side, you'll see a list of the accounts you have linked with eM Client. If you want to change the order of these accounts, simply select the one you want to move and use the Up and Down arrow buttons to move the account in the desired direction. This changes the order of your accounts on the main Mail tab.

Note: this is not the same as setting an account as default. Whichever account you have at the top will be the default account unless you've manually set another one to be the default. In this case, that account will still be the default account.