Outlookexpress6 Download Gmail

Hello
I would like to ask you if there is any solution for this problem I have just found.

It turns out that I have been using gmail with outlook express 6 for a while without any problem. Nonetheless, I have just experienced a problem I did not know about. It comes out when I send an email from my gmail account to the same gmail account by using external applications such as outlook express 6 or any other program coded by myself to send emails.

The problem is noticed because in contrast to any other email sent from any other email address to my gmail account, those emails which have only my gmail account as sender and recipient and at the same time have been sent by using outlook express or any other external application different than the web gmail, will not be downloaded to my outlook express6.

On the other hand if I send an email with the same gmail sender and gmail recipient but I use the web gmail application itself, then I will be able to download that email later by using outlook express6. It is an strange problem, but I am sure that some people will know about it.

I would appreciate any idea to be able to download from gmail to outlook express 6 those emails with the same gmail sender and recipient that were sent by using an external application such as outlook express or any other.
Thanks a lot.