This problem only occurs with the Postie plugin, not any other plugin or WP's system. I'm using Posting 1.4.5 on WP 3.4.2. Whenever I enter the mailserver settings and click "Save," I get sent to my site's 404 error page. Clicking back on the browser, refreshing, etc. gets me back to the settings, but nothing was saved in the mailserver info. When I try to re-enter it and save it, it's 404 once more.
Is this a problem with 1.4.5?