Mail client problems

[Guest]

[iii]

I want people on my network to be able to send/receive email from various clients (outlook express/thunderbird/etc)
At the moment I have the following setup:
SMTP Proxy enabled - green transparent, red inactive (spam and antivirus disabled until this issue is resolved)
POP Proxy disabled
HTTP Proxy enabled and using default settings

What I am getting is the following:
POP can send, but not receive
IMAP can receive, but not send

Clearly I am missing something in my configuration... and maybe up top too %(
Can anyone assist me in configuring this correctly?

Thanks in advance.

[EDIT]
Before I forget, I have not installed a local mail server.

[EDIT]
I thought I had it partially fixed, but I was wrong.
What is happening now is that mail sent through a mail client (Thunderbird/Outlook) is being flagged as spam.
I have checked the appropriate blacklisting sites and I am assured that my IP is not blocked.
My ISP also assures me that there is no problem from their side.
The issue only started after I installed EFW.
Reading more about blacklisting and the PBL, it appears that the issue is to do with mail authentication (port 587 vs unauthenticated port 25) and all unauthenticated e-mail is being flagged as spam.

Has anyone else had the same problem? (or have experience with the same issue?)
If so, please let me know where else I can look...

Thanks