I have two email accounts configured, an Exchange account which is also the DEFAULT account, and a POP3 account.

The problem is inconsistent default account behavior if "Group similar folders, such as Inboxes, from different accounts" under Preferences -> General is enabled.

It appears that the concept of a "default" account is quite meaningless

If "Group similar folders" is enabled, and I compose a new message, then the "From" header is taken from the account of the current selected message. i.e. if the currently selected message is from the POP3 account, then the "From" header of the NEW message will be from the POP3 account and not the default Exchange account.

However if "Group similar folders" is DISabled, and I select a message in the POP3 folder, then Outlook will correctly use the default Exchange account in the From header of any new messages.

In my opinion, this is a bug as Outlook should always use the default account as the sending (From) account regardless of the setting of "Group similar folders", otherwise the concept of a default account has no meaning.

I am currently running Outlook 2011 version 14.3.2 (130206).