when I connect to a POP3 account using Gmail, It shows POP3 Access Fails for that label
Here I attach a screenshot of the problem.
Error: Server is temporarily unavailable. Server returned error "Error in RETR command: no such message"
I suggest you to try with a different email client, I had similar problem with gmail, but i was able to solved that using sparrow in mac.
That´s Yahoo making our lives a little harder. I was able to use during a few months now the Yahoo account from Gmail. But today I started seeing that same error. There´s nothing you can do about it. Yahoo is blocking the Mail Fetcher. Here´s a discussion on that matter --> https://productforums.google.com/forum/#!topic/gmail/oUnb3ASPc0g
I had this issue today. I connected to the mail server with Thunderbird. Then, I deleted spam, deleted mysterious folders named .ERROR, removed everything in the trash folder, and compacted all folders. This allowed gmail to download my email again and fixed the error.
来源：https://stackoverflow.com/questions/18468085/connecting-to-pop3-with-gmail-fails