Not syncing new email

Since yesterday I have not been able to sync any new email. This is happening in the Mail app on my Windows 8 PC, Windows RT device, and Windows Phone.

I am able to successfully send email from all of those devices, but no new mail syncs. I am able to view all of the new email in Outlook.com. There is no error and on the Windows Phone the inbox claims "up to date." I have changed nothing on any of those devices. New calendar appointments however do sync instantaneously across all of the devices.

Here is what I have tried:

1. Manually syncing on all of the devices.
2. On my Windows Phone removing the email sync and adding it back. It took a long time to re-download all of my mail for each of the folders, but no new mail since yesterday morning.
3. Sent test messages from each of those devices. I can see the new email in my inbox on Outlook.com but they do not show up anywhere else.
4. Moved a few of the newer emails from the inbox to another folder via Outlook.com, but those messages in that folder still don't sync with any of the devices.

Again, I have changed nothing on all three of those devices or with my Outlook.com account.

Thanks for your assistance.