I've looked all through EE for this, and have tried a few things to no avail. One of our external workers freezes her browser about every fifth time she forwards or replies to any e-mail. It isn't only certain e-mails. The freeze is her browser waiting for a response from the server, I believe - it doesn't crash the browser, just hangs forever.
She can be reading the e-mail or just previewing it, doesn't make any difference.
We have Exchange 2000, she has IE 6.0.xxxx.xx. All latest patches applied. Problem started a month or so ago. Cannot replicate the problem on my account.