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. Instead, it uses the account associated with the mailbox or *.pst file the folder you are viewing is stored in. This change in behavior doesn't work well when an IMAP is configured to be the default email account and you have a POP3 account delivered to the default pst file.
This is another one of those areas where Outlook behaves differently depending on whether Outlook is running in Internet Mail Only (IMO) or Corporate/Workgroup (CW) mode. Outlook 97 has only one mode — the equivalent of Corporate/Workgroup. Beginning with Outlook 2002, Outlook is available in only one mode and offers the flexibility of the IMO
When you have an Exchange Server account in Small Business Server 2003 and Outlook is configured to use the POP3 account as default some users discover the SBS Exchange account is reset as the default account every time they reboot. This is caused by the SBS2003 logon script that configures the client computers when the