I originally was trying this one 3.7.1 but upgraded to 3.8 and am having the same issues today.
Alright so here is the story!
I was trying to get this plugin to work with my gmail to no avail. Gmail was blocking it's connections for security purposes (even though I enabled imap etc). I kept getting failures to connect for this reason.
So I tried an old yahoo account. IT WORKED! Like a charm!
I set up a new yahoo account for the website (it's not my website, don't want it using my email!). It wouldn't work. I would get a blank page when I'd try to "check now" and then I'd refresh and click "check now" again and be told to wait five minutes. I'd wait...sometimes a couple hours...try again, same issue.
I enabled SSL on that yahoo account and checked all the options between the one which worked and the one which didn't - everything was identical. I'd still get the 5 minute error. Even though the program is set to run every hour, I'd see no logs that it tried. (Let it sit over a day).
For kicks all I did was alter the login info to my old yahoo account and it was picking up posts, switched it to the new yahoo info and no dice.
Alright, so onto outlook. Figured maybe it was something in the 'new' yahoo mail since my last older one is years older. I created an outlook email. I enabled the pop3 (imap didn't seem to be allowed) and configured everything exactly how outlook said to.
I am getting the same 5 minute warning. I did change wp_debug to true and tried that. When I did this, it caused an error on the server (showed up at the top of the page) and whenever I tried to click "check now" it was just keep trying and would timeout, with no log showing. So I put it back to false and tried again. Same issue - blank page (or time out), refresh, click again and 5 minute error.
I let it sit for a few hours and even though it was set to check automatically twice since then, nothing shows up in the logs to show it actually tried. ;(
Thank you for any help you can give me!