Cannot reply to/forward mail over Wifi, only over EDGE

I have an iPhone 2G, 8GB, FW 2.2, jailbroken.

The Problem

• The iPhone is unable to reply to/forward any existing mails when it is connected over Wifi.
• However, it is able to send all existing and new mails when it is connected over EDGE.
• It is also able to send emails that originate from the iPhone; that is, I create a new email on my iPhone and send it.

Wifi Connection Is Not A Problem
I have 2 separate laptops connected to the Wifi, and the internet on both works fine. I am able to browse the net, and send and receive emails using multiple clients such as Outlook and Thunderbird. I am also able to browse the net using iPhone's Sarafi mobile browser, when connected to the Wifi.

Wifi Security Is Not A Problem
My Wifi is WPA-PSK secured, but I have the same problem even when I remove all wireless security (open).

Problem With All Mail Servers
I have multiple email accounts configured, including Gmail, AOL, Yahoo and several POP3 and IMAP servers. I am able to receive emails on ALL of them, but cannot reply to or forward any emails on ANY of them on the iPhone.
I am, however, able to send emails that are created on the iPhone, from the from all of them.

Has anyone faced this problem and found a solution? Or could someone please suggest a workaround?

Thanks in advance.