I have two accounts configured in Nokia Messaging, unfortunately the less important one is first in alphabet and therefore the default account when composing a new email...

Is there a way to set Nokia messaging standard account ?

Look in settings, there should be a way to change the default account...Although I am sure you could just go thru the account you want to send the mail thru

The default account setting lets you choose between Nokia Messaging or an other configures account, but not an account _inside_ Nokia messaging. I guess the solution is to exclude the less important account from Nokia messaging and configure it directly as IMAP account.