Server Unavailable error when manually processing or debugging

Emails with attached images are not being posted. Images are uploaded to media, and a draft post is created with no content. When I attempt to manually process, I get an error saying that the server is unavailable, 503. I get the same error if I select debug. See screenshot. I’m also including the test config details. If I clear out the mailbox and attempt a post with no attachment, it processes and posts normally.