When this happens to me I TELNET the mail server, and manually delete the offending mail item.
Instructions follow: (I have used mail.server.com to mean the name of your POP3 mail server)
If
you are using Windows 95 or Windows NT, you may launch Telnet from the Run
dialog box by choosing Start|Run, then enter:
telnet mail.server.com 110
and click OK.
If you are using another operating system or another Telnet program, check
the documentation or ask in the forum which supports that operating system
or Telnet program. The host is
mail.server.com
and the port is 110. You must connect to that port on that host to examine
your mailbox.
After the Telnet program connects, you will see this:
+OK NT POP3 Mail Server Ready
Unless you turn on local echo, everything you type from here on out
will not appear on the screen and the cursor will not move. To see
what you type, enable local echo from the Terminal > Preferences menu.
In the following steps, the <> is a placeholder; you do not enter the
angle brackets. None of the information you type is case-sensitive.
Enter: USER <username>
You will see: +OK
Enter: PASS <password> Your POP3 password
You will see: +OK
If you turn on logging, whatever you see on the screen will be logged to a
text file. To turn on logging, click TERMINAL|START LOGGING. The default
filename will be telnet.log and you can rename it if you like. Take note of
what directory the log file will be saved in, so you can find it afterward.
You can now enter specific commands.
LIST Lists message numbers and sizes.
RETR # Retrieves message number #. The message will scroll to the
screen. If you need to capture it, then logging should be
turned on. Note that this command does not delete messages
from the server.
TOP # nn Retreives the header and nn lines from message number #. This
command will allow viewing of the headers to confirm a specific
message is the one in question. Examples of usage:
TOP 3 10
will retrieve the headers and first ten lines of message #3
TOP 7 20
will retrieve the headers and first twenty lines of message #7.
The headers and requested number of lines will scroll to the
screen. To capture them, turn logging on. Note this command
does not delete messages from the server.
DELE # Deletes message number #. Critical for removing problem
messages. While still connected to the mailbox, further
attempts to access that message number will generate an
error. The next time you go into your POP3 mail via
normal procedures, the problem message(s) should be gone, and
all messages after the one deleted will find their message
number decremented by 1. For example, DELE 4 will cause
message #5 to become #4, message #6 to become #5, etc.
QUIT Quits the session (preferred over a File > Exit). If the
session is ended abnormally (such as using File > Exit),
the deleted messages will be restored.