Composing new email – change default ‘From’ address

Hello,

On my colleague's computer, she can send emails from different accounts.

Earlier today I had to rebuild her Outlook identity file. Just now we noticed that the 'From' field has defaulted to a different account than before.

How can we change the default 'From' address?

We tried rebooting, sending out a few emails from the address we'd like to be the default, restarting Outlook, all to no avail.

Thank you!