When you use Microsoft Outlook 2010 or Outlook 2013 and have multiple accounts delivered to different *.pst files, Outlook doesn't use the default account set in Account settings for new messages. Instead, it uses the account associated with the mailbox or *.pst file you have in focus. This change in behavior takes some getting used to, but its my experience that once they understand how it works, most users with multiple POP3 or Exchange accounts like it.

This feature not as well liked by users with an IMAP account as their primary account and POP3 accounts delivered to the default *.pst file. Instead of using the default IMAP account as it did in previous versions, Outlook now sends new mail using a POP3 account that is delivered to the *.pst. When the IMAP user sends a new message to a contact or starts a new message after viewing the calendar, Outlook chooses a POP3 account as the sending account.

The obvious solution is to use a different *.pst file for the POP3 accounts but if that is not acceptable, you can set a registry value to always use the default account, regardless of the data store, or to always ask which account to use. Both of these options are controlled by a registry key.

Alternately, you can use a macro to always open a new message with the default account selected or open a new message with a specific account selected.

Registry key in Outlook 2010 SP1 and up

When you have multiple accounts and an IMAP account in Outlook 2010/2013 and you change the default sending account to the IMAP account, you may experience the following issues:

• When you click a mailto link from a browser or from Outlook, the default sending account is the Exchange Server account instead of the IMAP account.
• When you create a new email message, the Exchange Server account is selected instead of the IMAP account.

Out of the box, Outlook 2010 SP1 and Outlook 2013 use the default account for Send to commands but not for new messages created while viewing a pst file (when a POP account is assigned to the pst file), unless you set a registry value to always force the use of the default account.

To force all new messages to use the default email account, regardless of which pst file you are viewing, browse to the following registry subkey and add a DWORD named NewItemsUseDefaultSendingAccount:

In Outlook 2016, the option was added to the UI (in File, Options, Mail) or you can set the key in the registry:

HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\Options\Mail
DWORD value: NewItemsUseDefaultSendingAccount
Value: 1

In Outlook 2013, the key is:

HKEY_CURRENT_USER\Software\Microsoft\Office\15.0\Outlook\Options\Mail
DWORD value: NewItemsUseDefaultSendingAccount
Value: 1

In Outlook 2010, edit this key:

HKEY_CURRENT_USER\Software\Microsoft\Office\14.0\Outlook\Options\Mail
DWORD value: NewItemsUseDefaultSendingAccount
Value: 1

If you prefer not to edit the registry yourself, you can run this registry file to set the NewItemsUseDefaultSendingAccount key:
Outlook 2016 Outlook 2013 Outlook 2010

Registry key to force account selection every time

This fix is simple, but can get annoying, fast, since it forces the user to select an account every time they send a new message. (Replies and Forwards always use the account the message arrived on.)

This might be good for people who use multiple accounts and frequently (accidentally) send using the wrong account, especially if they are sending sensitive documents, as it will almost eliminate accidentally sending email from the wrong account.

In Outlook 2016, the registry key is:

HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\16.0\outlook\options
Value Name: ForceAccountSelection
Value type: REG_DWORD: 1 for force, 0 to disable.

In Outlook 2013, the registry key is:

HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\15.0\outlook\options
Value Name: ForceAccountSelection
Value type: REG_DWORD: 1 for force, 0 to disable.

In Outlook 2010, the registry key is:

HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\14.0\outlook\options
Value Name: ForceAccountSelection
Value type: REG_DWORD: 1 for force, 0 to disable.

Notes: You need to create the path if it does not exist. You can also set this using the Office group policy templates. The value type is the same for both 32-bit and 64-bit Outlook.

If you don't want to edit the registry yourself, you can run this registry file to set the ForceAccountSelection key:

Outlook 2016 Outlook 2013 Outlook 2010

Warning: A user reported this tweak may prevent the New item buttons in Contacts and other folders from working.

Solution for default IMAP accounts: Create a fake POP3 account