A number of users have reported issues with Outlook today, and Microsoft's own Office 365 service status page shows that the company is aware of the issue and working on a fix.
From Microsoft:
We've identified that a subset of infrastructure was unable to process requests as expected, which caused general service availability to drop unexpectedly. We've redirected requests to alternate infrastructure to restore service, and we're monitoring the environment while connectivity recovers. Additionally, we're investigating an issue in which users are unable to send email messages.
The problem appears to have started in the early hours of the morning, but service should be restored soon. If you've been hit with connection problems, Microsoft says you should be able to find sent emails in your Drafts folder.
Thanks to amnesia for the tip!
