how do i switch from one account to another

You and your wife have to log-in to the own account.

Hope it helps.
Peter

Inside Evolution, you can go to Edit->Preferences and then you can check which account(s) do you want to be active.
This is going to merge the Inbox from your wife's account and yours.
Hope this helps, let me know.

If you share the same computer then consider setting up your Ubuntu installation so that your wife logs in as a separate user. Then she can configure her Evolution account to her own email address. This does not entail rebooting but merely switches users.

Alternatively, you might consider a separate computer exclusively for her use. There are some very good netbooks about.

Is there no way to have your mail viewed separately like Thunderbird or Outlook's concepts of "Identity"? The "create a separate user"-solution doesn't work if you're trying to easily differentiate between office emails and personal emails, without having to go into the _settings_. Is there some other concept that's supposed to be used to differentiate your emails, because going into your preferences doesn't really sound like a design _decision_ as much as a work around.