Cisco ASA 5500 & Thunderbird

Everthing use to work before installing a firewall at our site (Cisco ASA 5500). This started happening with one of my users, but now it happens on my home machine as well:

I launch Thunderbird and it checks for messages. After a minute, it times out with the server, failing to get any messages. After the first timeout, everything works fine. Outlook Express and Outlook

2000 both work fine.

If I setup Thunderbird with a different email account (outside our company), it works flawless.

Our Exchange server (5.5 sp4) is inside the firewall. The end user has no anti-virus or firewall running on the home pc.

I have tried uninstalling and reinstalling Thunderbird (including going to an older version).

I have run a packet capture program (wireshark) and the first time it shows a response of OK from Exchange, but it sends no user info. The next time, it shows a response of -ERR and then sends user info and works.

Any ideas?

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Just a little update:

Doing a packet capture on the good side (when TB works receiving email) shows that TB is sending a CAPA request, and then username, password, working fine.

The bad time (when it doesn't work the first time), TB does NOT send a CAPA request, it sends an AUTH request. Then it sends a couple more packets, and then it sends the FIN to end the connection.

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