About the only way is to telnet to the mail server on port 110 and log in to the mailbox. Then type list and press enter. Find the one with the large size and get the number before the size. Type dele ? where ? is the number of the message and press enter. This will delete the message from the mail server.
A 50k message shouldn’t take more than a few seconds to download, unless you have a very slow network connection.
This does not answer the question. See the reply by drummerlad