After having to throw away a chunk of coding today due to a flaky set of POP3 classes that wouldn't allow me access to message or attachment bodies, I have switched to using a new POP3 library which so far works a lot better - once I'd understood how it handled mailboxes and message attachments.
The current cut of the gateway code will now connect to a mailserver, and read all the email text (handling mail body text and text attachments), and then post it to Live Journal. This is a reasonable start, but I will need to think about controlling mail more effectively - for example using a message UIDL as a unique key to make sure that messages are only posted once - and handling some form of mail box purge. Of course, working to extract the attached JPG files is also important - and is on the to do list for tomorrow!
I've also added some debugging tools to the application itself - there's now a check button that connects to the mail server and lists its contents in a text pane in a standard Windows form - so I can at least now see what's on the mailserver. Chris at Wizards has been kind enough to set up a POP3 mailbox for my tests, so I can work on the code with out having to worry about filtering spam at this stage.
And I'm feeling quite good about where it's going, and what it's doing for my C# skills.