I do not think it is possible if your email server is strictly a POP3
server. Squirrel Mail is nothing more than a web interface to your Mail
Server. When you are using Squirrel Mail you are directly interfacing
with your mail server account. Outlook is only designed to go and pull
down those items in your inbox on your mail server. When sending a
message from Outlook the sent items folder directory resides on your
local computer not on your mail server and the vice-versa when you send
using the web interface of squirrel mail the sent items directory is
located on your mail server. Now if your email server has IMAP
capabilities then all of your email remains on the server so all
folders would be accessible whether you where using Outlook or Squirrel
Mail.