Cannot use POP3 and choose not to delete old messages

Issue Summary

Currently, if you use POP3 for a mailbox, and choose to not delete old messages, each time the mailbox is processed *all* of the messages (old and new) will be processed and recreated as objects (whether node, comment, etc) within Drupal. This is because there is no support in IMAP functions to get the UID of a message in a POP mailbox. There is a way to get what's called a UIDL for the POP message, but I don't believe it can be done through the IMAP PHP functions.

I propose we patch the module to provide help text and form validation to this regard on the new mailbox creation form. In the future maybe the module is changed to support POP and not deleting old items from the mailbox, but for now it could remain as unsupported. Does this sound reasonable?