I couldn't find anyone else in the posts who reported this, so just as an FYI:

I set up my Sprint Treo 600 with the HS POP3 Mail app; it's configured with one of my Comcast accounts (basic POP3/SMTP setup), and I had the checkbox setting "Leave Mail on Server" (under the Advanced tab) UNCHECKED. I have the mail app configured to automatically fetch the email, and download the maximum number of KB it allows (100k).

What happens? If someone emails me a message with a large attachment, approx the first 100k gets downloaded. When I open the email, and select the option to get the rest of it, I get a message stating that it's no longer on the server.

I guess they didn't code in enough logic to handle partial downloads. In short, keep the setting "Leave Mail on Server" checked.

Also: If there's an obvious config setting that I'm missing here (i.e., "loser error"), then let me know.